Severe cardiotoxicity during 5-fluorouracil chemotherapy: a case and literature report.

The chemotherapeutic agent 5-fluorouracil (5-FU) is a widely accepted part of many cancer treatment protocols. Its cardiotoxic potential is known, but considered uncommon and usually not life threatening, although some cases of severe cardiotoxicity related to 5-FU have been reported. The pathogenesis of cardiotoxicity caused by 5-FU is not clear. We report a case of sudden onset of severe cardiac failure, without ischemic symptoms or signs, during 5-FU treatment with serious consequences, in a previously healthy 23-year-old patient with squamous cell carcinoma of the tongue. Endomyocardial biopsy showed proliferation of the sarcoplasmic reticulum with marked vacuolization, similar to that found with doxorubicin cardiotoxicity. Because 5-FU cardiotoxicity is unpredictable and can have potentially fatal consequences, it requires, in our opinion, further clarification. With this well-documented case, including an endomyocardial biopsy, we hope to encourage additional efforts to investigate the pathophysiologic mechanisms of 5-FU cardiotoxicity.

Concomitant cisplatin/5-FU infusion and radiotherapy in advanced head and neck cancer: 8-year analysis of results.

BACKGROUND: The purpose of this study was to analyze long-term follow-up of a single institution's experience with a regimen of concomitant cisplatin/fluorouracil (5-FU) infusion and radiation given every other week. This analysis was stimulated by results of a randomized trial showing superiority for this regimen over induction cisplatin/5-FU chemotherapy followed by radiotherapy, especially in regional disease control. METHODS: All patients with stage III/IV disease who were referred by surgeons for nonoperative therapy and had a follow-up of at least 2 years were included. Concomitant chemoradiotherapy was administered days 1-5 of a 2-week treatment cycle, for a total of 7 cycles, with cisplatin 60 mg/m2 day 1, 5-FU 800 mg/m2 given over 24 hours days 1-5, and radiation 2 Gy days 1-5. RESULTS: Seventy-eight patients with stage III (n = 16) or IV (n = 62) were treated and followed for a median of 8 years. Six patients died during treatment, of aspiration pneumonia, sudden death, gastrointestinal bleeding, and stroke. When assessed 6 weeks after the end of treatment, 45 patients (63%) had no clinical evidence of disease, whereas 27 (37%) still had some persistent abnormality. However, 17 of these "partial responders" have not recurred. In all, 24 patients (31%) have recurred or progressed, 13 at the primary site, 5 after 3 years. None of 16 stage III and 24 (39%) of 62 stage IV patients ever progressed. Tongue and glottic larynx did best, with only 1 of 22 patients ever failing (none locally). Supraglottic and oral cavity cancers other than tongue had the worst failure rates. Nineteen patients (24%) died of other causes (DOC), tumor-free. Patients who DOC correlated strongly with T stage (p < .002) but not with N stage or with AJC stage. The 5-year progression-free survival was 60% (confidence interval [CI] = 49% to 72%), and overall survival was 43% (CI = 33% to 56%). CONCLUSIONS: Disease control for this advanced head and neck cancer population was excellent. This regimen was especially effective in advanced tongue and glottic cancers and all stage III disease sites. Advanced supraglottic and hypopharynx cancers are problematic. These, and especially T4 lesions, are associated with high DOC rates, possibly in part related to swallowing malfunction. Nevertheless, the long-term survival without surgical intervention was high with this regimen.

Integration of surgery in multimodality therapy for esophageal cancer.

BACKGROUND: While adding chemotherapy to radiation for the treatment of esophageal cancers has been shown to be beneficial, surgery usually follows treatment or is omitted. In either case, regional control remains problematic. The purpose of this study was to test the feasibility of using chemotherapy and radiation following surgery in the treatment of of esophageal cancer and to assess the impact of this approach on regional control and survival. PATIENTS AND METHODS: Twenty-five patients with esophageal cancer were treated in a phase I pilot protocol consisting of initial esophagectomy with gastroesophagostomy and subsequent combined chemotherapy and radiation. Chemotherapy consisted of cisplatin given on day 1 and 5-fluorouracil (FU) on days 1-5 by continuous infusion. Radiation therapy was administered in varying fractionation schedules of once or twice daily concomitantly with the chemotherapy. Treatment was repeated every other week for two to four cycles. Median follow-up was 42 months. RESULTS: Acute toxicities (mucositis and cytopenias) were common but not worse than grade 3. Higher doses of 50 Gy with 2 Gy b.i.d. hyperfractionation caused late complications in four of 10 patients, (two lethal). Control of local disease for all patients was excellent with only two known and two possible local recurrences (16%) but distant metastases were common (46%). Disease-free survival was 58 and 30% at 1 and 2 years, respectively. Survival was 58 and 32% at 1 and 2 years, respectively (median survival, 19 months). CONCLUSION: The local control rate and survival were better than those in our historical experience with cisplatin and 5-FU chemotherapy and radiation given prior to surgery. A dose-fractionation schedule of < 2 Gy up to a total of 50 Gy b.i.d. is recommended to avoid late adverse effects. The role of surgery will be defined by randomized studies. Better systemic therapy is needed to impact on systemic failure.

Continued malignant cell proliferation in head and neck tumors during cytotoxic therapy.

The effect of cytotoxic therapy on the proliferation of squamous cell carcinoma of the head and neck in vivo in patients was evaluated before and 15-35 days after the start of therapy. To accomplish this, iododeoxyuridine was administered at t = 0, and bromodeoxyuridine was administered 15-35 days later during treatment with a tumor biopsy obtained for study immediately after each pyrimidine infusion. Monoclonal antibodies specific for the halogenated pyrimidines were used to identify cells that were in the S-phase at the time of the infusions. Eleven patients were studied prior to treatment. Of those, the intratreatment biopsy of eight patients contained tumor tissue. In the other three patients, tumor tissue was not present in the second biopsy. Continued precursor incorporation into DNA-synthesizing cells during treatment was detected in six of eight tumor specimens. In two tumor specimens, an increase in the percentage of S-phase cells was noted, in two specimens tumor cells synthesizing DNA were not detected, and in four specimens the percentage of S-phase tumor cells was lower than that in the pretherapy specimen. Patients in whom there were no S-phase cells detected during treatment or in whom no tumor was detected in the second biopsy had a favorable treatment outcome in comparison to those patients in whom continued tumor proliferation during treatment was detected. The number of cells in S-phase prior to the initiation of treatment was not predictive of whether or not proliferation would continue during cytotoxic therapy. Evidence for reentry of kinetically quiescent cells into the cycle during treatment was noted. Additionally, cytotoxic therapy altered the proliferation pattern of normal-appearing mucosa as well. The results of this study demonstrate that tumor cell proliferation does continue in some squamous cell carcinoma of the head and neck during intensive cytotoxic therapy.

The dilemma of delayed cellulitis after breast conservation therapy.

OBJECTIVE: To determine the clinicopathologic characteristics of patients with breast cancers in whom delayed breast cellulitis developed after conservation therapy (lumpectomy, axillary dissection, and radiation). BACKGROUND: Breast cellulitis developing after conservation therapy represents a difficult diagnostic and management dilemma because determination of its origin may be necessary before further treatment decisions can be made. METHODS: In this retrospective evaluation of 184 sequential patients with breast cancers who underwent conservation therapy, 10 study patients (5%) in whom breast cellulitis developed 3 or more months after surgery were compared with the 174 patients in whom cellulitis did not develop. RESULTS: There was no significant difference in clinicopathologic characteristics of the study patients compared with control patients. The cellulitis resolved in 5 patients (50%) and persisted from 4 months to more than 1 year in 5 patients (50%). The cellulitis recurred in 1 patient who responded to repeated therapy. The 5 patients with persistent cellulitis underwent biopsies, and recurrent cancer was found in 1 patient. Recurrent cancer did not develop in the patients whose cellulitis resolved within 4 months with a minimum follow-up of 24 months. CONCLUSIONS: Delayed-onset cellulitis occurs in a small percentage of patients with breast cancers treated by conservation therapy. The cellulitis may take several weeks to clear, and/or it may recur or persist. If the condition persists after 4 months of therapy, a biopsy should be performed to rule out recurrent cancer.

Delaying the initiation of intact breast irradiation for patients with lymph node positive breast cancer increases the risk of local recurrence.

BACKGROUND: The impact of delaying irradiation to the intact breast for patients receiving chemotherapy for lymph node positive breast cancer is controversial. METHODS: From 1974 to 1989, 474 patients underwent lumpectomy and intact breast irradiation for early stage invasive breast cancer. Chemotherapy was administered to 84 patients (1 patient with bilateral breast cancer) because of positive axillary lymph nodes. Time from definitive breast surgery (lumpectomy or reexcision) to the initiation of breast irradiation was 21-314 days, with a median of 124 days. Forty-two patients began receiving radiation therapy before 120 days (early) and 42 more than 120 days after surgery (delayed). In the early group, cyclophosphamide/methotrexate/5-fluorouracil (CMF) was administered to 32 patients, doxorubicin, cyclophosphamide or cyclophosphamide, doxorubicin, 5-fluorouracil (AC or CAF) to 6 patients, and other regimens to 4 patients; in the delayed group, CMF was given to 29 patients, CAF to 12 patients, and L-PAM/5-fluorouracil to 1 patient. RESULTS: Median follow-up was 62 months. There was one breast recurrence in the early group, compared with six in the patients receiving delayed irradiation. The actuarial relapse rates for these groups at 5 years were 2% and 14%, respectively (P = 0.05). Survival and distant disease free survival were not significantly different between the two groups. CONCLUSIONS: Delays in the initiation of irradiation are associated with increased risk of relapse in the breast. When possible, the interval between definitive breast surgery (lumpectomy or reexcision) and the initiation of radiation therapy should be fewer than 120 days.

Omission of axillary lymph node dissection in early-stage breast cancer: effect on treatment outcome.

PURPOSE: To determine the effect omission of axillary lymph node dissection has on outcome in patients treated with breast-conserving therapy for early-stage invasive breast cancer. MATERIALS AND METHODS: The authors evaluated 492 patients with breast cancer treated with (n = 32) and without (n = 456) axillary lymph node dissection. The primary tumor characteristics of the two groups were similar, though the median age was different. All patients received whole-breast radiation (mean dose, 50 Gy); additional tumor bed boosts and nodal irradiation were used more often in patients without dissection. RESULTS: Median follow-up in patients without and with dissection was 60 and 52 months, respectively. The 5-year survival was 88% and 93%, respectively. There were no regional failures in the group treated without dissection. Crude rates of local and distant failure were similar for both groups. CONCLUSION: Omission of axillary lymph node dissection should be considered in patients whose pathologic nodal status will not influence decisions regarding adjuvant therapy.

Using simulation data to predict lung geometry for inhomogeneity corrections in breast cancer treatments.

PURPOSE: To develop a statistical model based only on simulation measurement data, to predict the lung geometry in the central slice of the tangential radiation treatment fields for breast cancer. METHODS AND MATERIALS: A linear regression analysis was performed on 22 patients to determine the shape of lung in the central axis plane of the tangential radiation fields. Data collected include the greatest perpendicular distance (GPD) measured from the chest wall to the field border on computed tomography (CT) images, the central lung distance (CLD) measured from the posterior field border to the chest wall on the simulation portal images, and the lung contours digitized at 1 cm intervals. The lung contours of these patients were fitted to a parabolic curve through a polynomial regression model. A lung template based on the regression model is used to construct a "generic lung" contour on patients' external body contours for treatment planning. The accuracy of this technique was tested on another group of 15 patients for its ability to predict the shape of lung on the central axis plane and the accuracy of dose to the prescription point. RESULTS: The polynomial regression indicates that all the patients' lung contours in the tangential fields follow a parabolic curve: Y = -0.0808 X2 + 0.0096 X + 0.0326. The maximum lung involvement (GPD) can be determined from the value of CLD measured on the simulation film by the linear regression model with a determination coefficient of 0.712. The 15-patient test results indicate that our model predicts the lung separation on the central axis with an average deviation of 1.35 cm, and the average absolute dose deviation to the dose prescription point is 1.46%. CONCLUSION: The model presented in this article provides an efficient method to estimate the lung geometry for breast cancer treatment planning without the requirement of CT data. The lung contour predicted by our model is useful for calculating dose distributions with inhomogeneity correction and may potentially benefit patients at higher risk of pulmonary toxicity.

Cell kinetics of head and neck cancers.

We measured the tumor cell proliferative rate in 26 patients with head and neck cancer, 22 of which were squamous cell carcinomas (SCCs). Patients received sequential infusions of iododeoxyuridine and bromodeoxyuridine, after which the tumor was biopsied and studied. The percentage of labeled cells [labeling index (LI)] in well-differentiated SCCs was 20.4 +/- 2.7% (mean +/- SE) and 23.8 +/- 2.1% in moderately differentiated SCCs (P = 0.135). The LIs of two poorly differentiated SCCs were 39.4 and 55.9%. The LI was 2.5% in a high-grade lymphoepithelioma and 24.8% in a malignant lymphoma. In one well-differentiated and one poorly differentiated mucoepidermoid tumor, the LIs were 3.0% and 29.1%, respectively. S-phase duration time measurements ranged from 5.1-21.5 h (12.8 +/- 1.5). The calculated potential doubling times ranged from 18.8-84.5 h (47.3 +/- 6.7). The duration of G2 was between 90 and 180 min. To track the fate of labeled cells, in four patients a repeat biopsy was obtained 7-14 days after the iododeoxyuridine/bromodeoxyuridine infusion. These patients did not receive treatment between the biopsies. Due to the dilution of the label, most labeled cells in the second biopsy demonstrated a "fragmented" pattern resulting from repeated cell divisions. In two patients, however, 25% of cells in the second biopsy had undiluted label, suggesting that these cells had not divided after incorporating iododeoxyuridine/bromodeoxyuridine. On Day 7 labeled cells migrated to keratinized parts of tumors and to necrotic foci. Thus, the arrest of cell cycle transition, tumor cell differentiation, and cell death may be major routes of tumor cell loss from the proliferative compartment. This may explain the difference between very short potential doubling times and the actual rate of tumor growth.

Should multicentric disease be an absolute contraindication to the use of breast-conserving therapy?

PURPOSE: Multicentric cancer is present in a large proportion of mastectomies performed as treatment of breast cancer; it has been considered a contraindication to breast conservation. METHODS AND MATERIALS: We reviewed the records of our patients with Stage I or II breast cancer treated with breast conserving surgery and radiation therapy over a 13-year period. Twenty-seven patients had two or more nodules of grossly visible cancer separated by histologically normal breast tissue. All patients had grossly negative margins of excision; however, four patients had microscopically positive margins. Nine patients had positive axillary nodes. All patients received radiation therapy to the breast postoperatively, with a median dose of 50.4 Gy in 28 fractions; 11 patients also received a boost dose of 6-20 Gy to the tumor bed. Eleven patients were given adjuvant chemotherapy and one patient was given adjuvant tamoxifen. RESULTS: With a median follow-up of 53 months, only one patient has relapsed in the breast (3.7%); that patient relapsed in multiple distant sites at the same time. Three patients have died of disseminated disease; the actuarial survival and disease-free survival rates at 4 years are 89%. CONCLUSION: Breast conservation may be considered for patients with multicentric breast cancer discovered at the time of histologic examination. For patients with multicentric disease detected prior to surgery, breast conserving therapy may be appropriate as long as: (1) all clinically and radiographically apparent abnormalities are removed, (2) clear margins of resection are achieved, and (3) there is no extensive intraductal component.

Primary radiation therapy to T1 and T2 breast cancer following conservative surgery. Which patients should be boosted?

We reviewed 199 radiated patients at our institution (201 breasts treated) and its affiliates treated between 1978 and 1989. Of these, 157 were T1 and T2 invasive breast carcinoma. Our intent was to retrospectively compare the results of those who received standard doses of 4,500 to 5,000 cGy to the breast to those that received an additional boost to the surgical bed to a dose totaling at least 5,500 cGy. There were a total of 5 local recurrences in 159 treated breasts. (The mean follow-up time was 36 months.) Of our T1 and T2 patients with clear resection margins that were boosted, there was 1 local recurrence in 28 treated breasts. There was 1 local recurrence in the nonboosted group of 68 patients. Except for one patient, all patients with positive margins were boosted. There were 2 local recurrences in the 23 T1 and T2 breasts with positive margins that were boosted. Of the patients with uncertain margins who were not boosted, there was one local recurrence in 20 treated breasts. Of those with uncertain margins that were boosted, there were no local recurrences in 19 treated breasts. From our results, it would appear that a boost to the primary site is unnecessary if the margins of resection are negative (by either inking or if it is clearly stated in the pathology report). In those patients with uncertain margins, most were done in the years before margins were routinely inked, but generous excisional biopsies were usually done. In this latter group of patients, there also was no added benefit to boosting.

Long-term results of curative irradiation in pathologically staged IA and IIA Hodgkin disease.

One hundred seventy-six patients with pathologically staged IA and IIA Hodgkin disease (HD) treated with irradiation alone were evaluated for long-term survival and freedom from relapse (FFR). Most of the patients received treatment to mantle and paraaortic fields; chemotherapy was not given except as salvage therapy. For pathologically staged IA disease, the 5-, 10-, and 15-year survival rates were 94%; the corresponding FFR rates were 96%, 93%, and 93%. For pathologically staged IIA disease, respective survival rates were 93%, 89%, and 80%, with FFR rates of 86%, 84%, and 84%. Twenty-one patients (12%) had relapse of HD; salvage therapy was successful in 11 of these patients. Pelvic recurrence was uncommon (three of 176 cases [2%]). No patient developed leukemia, and only two patients developed second malignancies (lung cancer in both cases). The authors conclude that radiation therapy is effective in treatment of early-stage HD.

Radiation-induced sarcoma of the thyroid.

A 23-year-old white man presented with a thyroid mass 12 years after receiving high-dose radiotherapy for a T2 and N1 lymphoepithelioma of the nasopharynx. Following subtotal thyroidectomy, a histopathologic examination revealed liposarcoma of the thyroid gland. The relationship between sarcomas and irradiation is described and Cahan and colleagues' criteria for radiation-induced sarcomas are reviewed. To our knowledge, we are presenting the first such case of a radiation-induced sarcoma of the thyroid gland.

Combined simultaneous cisplatin/fluorouracil chemotherapy and split course radiation in head and neck cancer.

Fifty-three patients with stage III (eight patients, 15%), stage IV (36 patients, 68%), or recurrent disease (nine patients, 17%) entered a study of simultaneous cisplatin, 60 mg/m2 day 1, fluorouracil (5-FU) infusion, 800 mg/m2 days 1 to 5, and radiation, 2 Gy days 1 to 5, every other week for a total of seven cycles (70 Gy in 13 weeks). Patient acceptance was high, with only two patients (4%) refusing to complete therapy. The median actual dose delivered was 88% of the planned dose for cisplatin, 78% for 5-FU, and 70 Gy for radiation. Weight loss of 10% or more and severe mucositis were the most common side effects (53% and 48% incidence, respectively). All patients were followed at least 1 year (median, 51 months). While the complete response rate (55%) seemed no better than that reported in other series, freedom of progression of regional disease (73%), and the survival of all patients (median, 37 months) were substantially improved. Only 33% of partial responders have failed regionally, while 15% of complete responders have failed regionally (P greater than .10), which indicates that clinical assessment of response was unreliable. Stage, the presence of N3 disease, and delivery of less than the median actual dose received of 5-FU (but not cisplatin) were significantly associated with failure. This regimen is feasible and tolerable in this difficult patient population. It generally requires no special forced feeding techniques. Survival results from this limited institution study appear better than those using sequential multimodality therapies. With such favorable regional control, this approach may offer an alternative in the future to radical surgery and radiation in resectable disease. More definitive evaluation seems warranted.

Radiation therapy in the management of rectal cancer.

For many years, rectal carcinoma has been treated by surgery alone. However, survival rates have not improved historically and local recurrence remains a problem. Adjuvant radiation therapy does have a role in this disease. While the optimal scheduling and dose are not determined yet, it can certainly prevent local recurrence and potentially increase survival. There are advantages to delivering radiation therapy preoperatively and postoperatively and the combination of low-dose preoperative radiation therapy and postoperative radiation therapy in selected patients ("sandwich" therapy) appears promising. The use of chemotherapy in combination with radiation therapy may further improve survival rates. Care must be taken in patients treated with rectal carcinoma to minimize the normal tissue irradiated to decrease complications and deliver tumoricidal doses to the areas at risk. Techniques are available to both the surgeon and the radiation oncologist to minimize the amount of small bowel irradiated. Radiation therapy also has a role in the treatment of very early rectal cancers as part of a sphincter-saving procedure and in the treatment of advanced or recurrent rectal cancers. In the latter, intraoperative radiation therapy plays an important role in controlling recurrent or residual rectal cancer.

The 5-year results of a randomized trial of adjuvant radiation therapy after chemotherapy in breast cancer patients treated with mastectomy.

The use of adjuvant radiation therapy in breast cancer patients treated with mastectomy and adjuvant chemotherapy has been controversial. In order to assess the necessity and effectiveness of adjuvant radiation therapy in this setting, we reviewed the results in 510 patients with T1-T3 tumors and pathologically positive nodes or tumors larger than 5 cm and negative nodes who were treated with adjuvant chemotherapy. Patients with four or more positive nodes or at least one positive apical node were randomized to receive either five or ten cycles of cyclophosphamide/Adriamycin (Adria Laboratories, Columbus, OH) (CA) and patients with one to three positive nodes or operable tumors larger than 5 cm and pathologically negative nodes were randomized to receive eight cycles of either cyclophosphamide, methotrexate, and 5-fluorouracil (5-FU) (CMF) or methotrexate and 5-FU (MF) chemotherapy. Two hundred six of these patients were subsequently rerandomized to receive either no further treatment or adjuvant radiotherapy. Thirty-five patients withdrew after randomization, including 34 who declined to receive radiotherapy. Radiation therapy consisted of 4,500 cGy in 5 weeks to the chest wall and appropriate draining lymph nodes. Median follow-up from chemotherapy randomization is 45 months for patients in the CA arm and 53 months for those in the CMF/MF arm. The crude rate of local failure (chest wall or draining lymph node areas) as first site of failure for patients randomized to receive chemotherapy only was 14%; for those randomized to receive both chemotherapy and radiotherapy it was 5% (P = .03). For patients in the CMF/MF arm, the rate of local failure as the first site of failure was nearly the same for patients randomized to chemotherapy only as for those randomized to adjuvant radiotherapy as well (5% v 2%). For patients in the CA arm, the crude rate of local failure was 20% for patients randomized to receive chemotherapy only, and 6% for those randomized to both types of adjuvant treatment (P = .03). Among the 43 patients treated with CA who actually received radiotherapy, there was only one local failure, compared with 12 local failures among the 59 patients (20%) who actually did not receive radiotherapy (P = .007). No significant difference was seen in disease-free survival or overall survival in either the CA or the CMF/MF arm between patients randomized to receive radiation therapy and those randomized to no further treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Work in progress: radioprotection of human breast cancer cells by elevation of intracellular cyclic AMP.

MCF-7 human breast cancer cells that were treated for one hour prior to X irradiation with the cyclic AMP-inducing agent 1-methyl-3-isobutylxanthine displayed a slight but significant increase in surviving fraction over untreated controls at each radiation dose level. This was accompanied by a two-fold increase in the level of intracellular cyclic AMP.

DNA of Epstein-Barr virus. V. Direct repeats of the ends of Epstein-Barr virus DNA.

Previous data indicated that Epstein-Barr virus DNA is terminated at both ends by direct or inverted repeats of from 1 to 12 copies of a 3 X 10(5)-dalton sequence. Thus, restriction endonuclease fragments which include either terminus vary in size by 3 X 10(5)-dalton increments (D. Given and E. Kieff, J. Virol. 28:524--542, 1978; S. D. Hayward and E. Kieff, J. Virol. 23:421--429, 1977). Furthermore, defined fragments containing either terminus hybridize to each other (Given and Kieff, J. Virol. 28:524--542, 1978). The 5' ends of the DNA are susceptible to lambda exonuclease digestion (Hayward and Kieff, J. Virol. 23:421--429, 1977). To determine whether the terminal DNA is a direct or inverted repeat, the structures formed after denaturation and reannealing of the DNA from one terminus and after annealing of lambda exonuclease-treated DNA were examined in the electron microscope. The data were as follows. (i) No inverted repeats were detected within the SalI D or EcoRI D terminal fragments of Epstein-Barr virus DNA. The absence of "hairpin- or pan-handle-like" structures in denatured and partially reannealed preparations of the SalI D or EcoRI D fragment and the absence of repetitive hairpin- or pan-handle-like structures in the free 5' tails of DNA treated with lambda exonuclease indicate that there is no inverted repeat within the 3 X 10(5)-dalton terminal reiteration. (ii) Denatured SalI D or EcoRI D fragments reanneal to form circles ranging in size from 3 X 10(5) to 2.5 X 1O(6) daltons, indicating the presence of multiple direct repeats within this terminus. (iii) Lambda exonuclease treatment of the DNA extracted from virus that had accumulated in the extracellular fluid resulted in asynchronous digestion of ends and extensive internal digestion, probably a consequence of nicks and gaps in the DNA. Most full-length molecules, after 5 min of lambda exonuclease digestion, annealed to form circles, indicating that there exists a direct repeat at both ends of the DNA. (iv) The finding of several circularized molecules with small, largely double-strand circles at the juncture of the ends indicates that the direct repeat at both ends is directly repeated within each end. Hybridization between the direct repeats at the termini is likely to be the mechanism by which Epstein-Barr virus DNA circularizes within infected cells (T. Lindahl, A. Adams, G. Bjursell, G. W. Bornkamm, C. Kaschka-Dierich, and U. Jehn, J. Mol. Biol. 102:511-530, 1976).