A validated scoring system to identify long-term survivors after radiotherapy for metastatic spinal cord compression.

PURPOSE: This study aimed to develop and validate a scoring system to identify long-term survivors after conventional radiotherapy (RT) for metastatic spinal cord compression (MSCC). PATIENTS AND METHODS: Data from 1,125 patients who had received long-course RT for MSCC were included in this study. Of these patients, 344 survived for over 12 months and 781 died within a year following RT. Based on differences between the distributions of patient characteristics in the two groups, a scoring system was developed. Scores ranged from 0 to 18 points and 15 points was selected as the cutoff for identifying long-term survivors. Data from the 1,125 long-course RT patients (test group) were compared to data from 773 patients receiving short-course RT (validation group). RESULTS: A score of ≥ 15 points was associated with a 94 % proportion of long-term survivors. The 15-point cutoff resulted in a specificity of 98 % and a positive predictive value of 94 % for identification of long-term surviving patients. The proportions of long-term survivors for each scoring point in the validation group were very similar to those in the test group. CONCLUSION: This new scoring system enabled identification of long-term survivors after RT for MSCC with very high specificity and positive predictive value. The score proved to be valid and reproducible.

Prognostic factors and a survival score for patients with metastatic spinal cord compression from colorectal cancer.

BACKGROUND: This study aimed to identify independent prognostic factors and to create a survival score for patients with metastatic spinal cord compression (MSCC) from colorectal cancer (CRC). PATIENTS AND METHODS: Data from 121 patients irradiated for MSCC from CRC were retrospectively analyzed. Eleven potential prognostic factors were investigated including tumor type, age, gender, Eastern Cooperative Oncology Group performance status score (ECOG-PS), number of involved vertebrae, ambulatory status prior to radiotherapy (RT), other bone metastases, visceral metastases, interval from cancer diagnosis to RT of MSCC, time of developing motor deficits prior to RT, and the RT schedule. RESULTS: On multivariate analysis, improved motor function was significantly associated with an ECOG-PS of 1-2 (p = 0.011) and a slower development of motor deficits (p < 0.001). Improved local control was significantly associated with absence of visceral metastases (p = 0.043) and longer-course RT (p = 0.008). Improved survival was significantly associated with an ECOG-PS of 1-2 (p < 0.001), ambulatory status (p < 0.001), absence of visceral metastases (p < 0.001), and a slower development of motor deficits (p = 0.047). These four prognostic factors were included in a survival score. The score for each factor was determined by dividing the 6-month survival rate by 10. The prognostic score represented the sum of the factor scores. Four prognostic groups were designed; the 6-month survival rates were 0% for 8-12 points, 26% for 13-18 points, 62% for 20-23 points, and 100% for 24-27 points (p < 0.001). CONCLUSION: This study identified several independent prognostic factors for treatment outcomes in patients irradiated for MSCC from CRC. The survival prognosis of these patients can be estimated with a new score.

Impact of zoledronic acid on control of metastatic spinal cord compression.

BACKGROUND: Zoledronic acid was demonstrated to reduce the rate of skeletal-related events, a hypernym including various outcomes, in patients with bone metastases. In contrast to other studies, this matched-pair analysis focused solely on the impact of zoledronic acid on metastatic spinal cord compression (MSCC). PATIENTS AND METHODS: Data from 98 patients with MSCC receiving radiotherapy plus zoledronic acid were matched 1:2 to 196 patients receiving radiotherapy alone for ten potential prognostic factors. Both groups were compared for local control of MSCC within the irradiated region, overall control of MSCC (local and distant MSCC control), and survival. RESULTS: The 1-year local control rates were 90% after radiotherapy plus zoledronic acid and 81%, after radiotherapy alone (p = 0.042). The 1-year overall control rates were 87% and 75%, respectively (p = 0.016), and the 1-year survival rates were 60% and 52%, respectively (p = 0.17). Results were significant in the Cox proportional hazards model regarding local control (p = 0.024) and overall control (p = 0.008). CONCLUSION: According to the results of this study, zoledronic acid was associated with improved control of MSCC in irradiated patients.

A survival score for patients with metastatic spinal cord compression from prostate cancer.

BACKGROUND: This study aimed to develop and validate a survival scoring system for patients with metastatic spinal cord compression (MSCC) from prostate cancer. PATIENTS AND METHODS: Of 436 patients, 218 patients were assigned to the test group and 218 patients to the validation group. Eight potential prognostic factors (age, performance status, number of involved vertebrae, ambulatory status, other bone metastases, visceral metastases, interval from cancer diagnosis to radiotherapy of MSCC, time developing motor deficits) plus the fractionation regimen were retrospectively investigated for associations with survival. Factors significant in the multivariate analysis were included in the survival score. The score for each significant prognostic factor was determined by dividing the 6-month survival rate (%) by 10. The total score represented the sum of the scores for each factor. The prognostic groups of the test group were compared to the validation group. RESULTS: In the multivariate analysis of the test group, performance status, ambulatory status, other bone metastases, visceral metastases, and interval from cancer diagnosis to radiotherapy were significantly associated with survival. Total scores including these factors were 20, 21, 22, 24, 26, 28, 29, 30, 31, 32, 33, 35, 37, or 39 points. In the test group, the 6-month survival rates were 6.5% for 20-24 points, 44.6% for 26-33 points, and 95.8% for 35-39 points (p < 0.0001). In the validation group, the 6-month survival rates were 7.4%, 45.4%, and 94.7%, respectively (p < 0.0001). CONCLUSIONS: Because the survival rates of the validation group were almost identical to the test group, this score can be considered valid and reproducible.

Prognostic factors for local control and survival in patients with spinal cord compression from myeloma.

BACKGROUND: This retrospective study aimed to identify prognostic factors for local control and survival in 214 patients irradiated for spinal cord compression (SCC) from myeloma. PATIENTS AND METHODS: Ten potential prognostic factors were investigated including age, gender, Eastern Cooperative Oncology Group performance score (ECOG-PS), number of involved vertebrae, ambulatory status, other osseous lesions, extraosseous lesions, interval from first diagnosis of myeloma to SCC, time developing motor deficits before radiotherapy (RT), and the RT schedule (short-course vs. long-course RT). RESULTS: On univariate analysis, no factor was associated with local control of SCC. Survival was associated with ECOG-PS (p < 0.001), ambulatory status (p < 0.001), other osseous lesions (p < 0.001), and extraosseous lesions (p < 0.001). On multivariate analysis, these prognostic factors maintained significance. CONCLUSION: New independent prognostic factors were identified for survival after RT of SCC from myeloma. These factors can help tailor treatment to the individual patient.

Metastatic spinal cord compression in non-small cell lung cancer patients. Prognostic factors in a series of 356 patients.

BACKGROUND: Patients with metastatic spinal cord compression (MSCC) from non-small cell lung cancer (NSCLC) have an unfavorable prognosis compared to most other MSCC patients. This study was performed to identify prognostic factors for functional outcome and survival in these patients after radiotherapy (RT) alone. PATIENTS AND METHODS: Data of 356 patients irradiated for MSCC from NSCLC were retrospectively analyzed. Ten potential prognostic factors were investigated including age, gender, Eastern cooperative Oncology Group performance score (ECOG-PS), number of involved vertebrae, pre-RT ambulatory status, other bone metastases, visceral metastases, interval from cancer diagnosis to RT of MSCC, time developing motor deficits before RT, and the radiation schedule. RESULTS: On multivariate analysis, better functional outcome was associated with pre-RT ambulatory status (estimate: - 0.84, p = 0.022), no visceral metastases (estimate: - 1.15, p < 0.001), interval from cancer diagnosis to RT of > 15 months (estimate: + 0.48, p = 0.019), and slower (> 7 days) development of motor deficits (estimate: + 1.56, p < 0.001). On multivariate analysis, improved survival was significantly associated with female gender (risk ratio (RR) 1.32, p = 0.043), ECOG-PS 1-2 (RR 1.45, p = 0.034), pre-RT ambulatory status (RR 0.58, p < 0.001), no other bone metastases (RR 1.38, p = 0.010), no visceral metastases (RR 2.87, p < 0.001), interval from cancer diagnosis to RT of > 15 months (RR 0.84, p = 0.035), and slower (> 7 days) development of motor deficits (RR 0.78, p < 0.001). CONCLUSION: This study identified additional independent prognostic factors for outcomes after radiotherapy of MSCC from NSCLC. These prognostic factors can be used for stratification in future trials and can help develop prognostic scores for MSCC from NSCLC.

Prognostic factors in a series of 504 breast cancer patients with metastatic spinal cord compression.

BACKGROUND: This study was performed to identify new significant prognostic factors in breast cancer patients irradiated for metastatic spinal cord compression (MSCC). PATIENTS AND METHODS: The data of 504 patients with breast cancer patients with MSCC were retrospectively analyzed with respect to posttreatment motor function, local control of MSCC, and survival. The investigated potential prognostic factors included age, Eastern Cooperative Oncology Group (ECOG) performance score, number of involved vertebrae, other bone metastases, visceral metastases, pretreatment ambulatory status, interval from cancer diagnosis to radiotherapy of MSCC, time developing motor deficits before radiotherapy, and the radiation schedule. RESULTS: On multivariate analysis, better functional outcome was associated with ambulatory status prior to RT (estimate - 1.29, p < 0.001), no visceral metastases (estimate - 0.52, p = 0.020), and slower development of motor deficits (estimate + 2.47, p < 0.001). Improved local control was significantly associated with no other bone metastases (risk ratio (RR) 4.33, 95% confidence interval (CI) 1.36-14.02, p = 0.013) and no visceral metastases (RR 3.02, 95% CI 1.42-6.40, p = 0.005). Improved survival was significantly associated with involvement of only 1-2 vertebrae (RR 1.27, 95% CI 1.01-1.60, p = 0.044), ambulatory status before radiotherapy (RR 1.75, 95% CI 1.23-2.50, p = 0.002), no other bone metastases (RR 1.93, 95% CI 1.18-3.13, p = 0.009), no visceral metastases (RR 7.60, 95% CI 5.39-10.84, p < 0.001), and time developing motor deficits before radiotherapy (RR 1.55, 95% CI 1.30-1.86, p < 0.001). CONCLUSION: Several new independent prognostic factors were identified for treatment outcomes. These prognostic factors should be considered in future trials and may be used to develop prognostic scores for breast cancer patients with MSCC.

Resection plus whole-brain irradiation versus resection plus whole-brain irradiation plus boost for the treatment of single brain metastasis.

BACKGROUND: The optimal treatment for patients with a single brain metastasis is controversial. This study investigated the value of a radiation boost given in addition to neurosurgerical resection and whole-brain irradiation (WBI). PATIENTS AND METHODS: In this retrospective study, outcome data of 105 patients with a single brain metastasis receiving metastatic surgery plus WBI (S + WBI) were compared to 90 patients receiving the same treatment plus a boost to the metastatic site (S + WBI + B). The outcomes that were compared included local control of the resected metastasis (LC) and overall survival (OS). In addition to the treatment regimen, eight potential prognostic factors were evaluated including age, gender, performance status, extent of metastatic resection, primary tumor type, extracerebral metastases, recursive partitioning analysis (RPA) class, and interval from first diagnosis of cancer to metastatic surgery. RESULTS: The LC rates at 1 year, 2 years, and 3 years were 38%, 20%, and 9%, respectively, after S + WBI, and 67%, 51%, and 33%, respectively, after S + WBI + B (p = 0.002). The OS rates at 1 year, 2 years, and 3 years were 52%, 25%, and 19%, respectively, after S + WBI, and 60%, 40%, and 26%, respectively, after S + WBI + B (p = 0.11). On multivariate analyses, improved LC was significantly associated with OP + WBI + B (p = 0.006) and total resection of the metastasis (p = 0.014). Improved OS was significantly associated with age ≤ 60 years (p = 0.028), Karnofsky Performance Score > 70 (p = 0.015), breast cancer (p = 0.041), RPA class 1 (p = 0.012), and almost with the absence of extracerebral metastases (p = 0.05). CONCLUSION: A boost in addition to WBI significantly improved LC but not OS following resection of a single brain metastasis.

Equivalence of hyperfractionated and continuous brachytherapy in a rat tumor model and remarkable effectiveness when preceded by external irradiation.

PURPOSE: In clinical brachytherapy, there is a tendency to replace continuous low-dose-rate (LDR) irradiation by either single-dose or fractionated high-dose-rate (HDR) irradiation. In this study, the equivalence of LDR treatments and fractionated HDR (2 fractions/day) or pulsed-dose-rate (PDR, 4 fractions/day) schedules in terms of tumor cure was investigated in an experimental tumor model. METHODS AND MATERIALS: Tumors (rat rhabdomyosarcoma R1M) were grown s.c. in the flank of rats and implanted with 4 catheters guided by a template. All interstitial radiation treatment (IRT) schedules were given in the same geometry. HDR was given using an (192)Ir single-stepping source. To investigate small fraction sizes, part of the fractionated HDR and PDR schedules were applied after an external irradiation (ERT) top-up dose. The endpoint was the probability of tumor control at 150 days after treatment. Cell survival was estimated by excision assay. RESULTS: Although there was no fractionation effect for fractionated HDR given in 1 or 2 fractions per day, TCD(50)-values were substantially lower than that for LDR. A PDR schedule with an interfraction interval of 3 h (4 fractions/day), however, was equivalent to LDR. The combination of ERT and IRT resulted in a remarkably increased tumor control probability in all top-up regimens, but no difference was found between 2 or 4 fractions/day. Catheter implantation alone decreased the TCD(50) for single-dose ERT already by 17.4 Gy. Cell viability assessed at 24 h after treatment demonstrated an increased effectiveness of interstitial treatment, but, after 10 Gy ERT followed by 10 Gy IRT (24-h interval), it was not less than that calculated for the combined effect of these treatments given separately. CONCLUSION: In full fractionation schedules employing large fractions and long intervals, the sparing effect of sublethal damage repair may be significantly counteracted by reoxygenation. During 3-h intervals, however, repair may be largely completed with only partial reoxygenation causing PDR schedules to be less effective than fractionated HDR, and equivalent to LDR. Brachytherapy with clinically sized fractions after a large external top-up dose showed a remarkable increase in tumor control rate with no effect of fractionation (up to 4 fractions/day), which could not be fully explained by differences in dose distribution or in the cell viability assessed after treatment. This suggests a longer lasting effect on cell survival or radiosensitivity associated with catheter implantation shortly after the top-up dose.

Reirradiation of primary brain tumours: survival, clinical response and prognostic factors.

BACKGROUND AND PURPOSE: First, the aim was to determine the survival and quality of life after reirradiation of relapsing primary malignant brain tumours. The second aim was to assess the influence of a set of potentially prognostic factors on survival. MATERIALS AND METHODS: Forty-two patients received reirradiation for recurring primary brain tumours. The interval between the two consecutive treatments was at least 1 year. External beam irradiation for the initial and recurrent tumour was usually delivered with two opposing lateral fields or two wedged fields in orthogonal directions. The median physical doses of the first and second radiation course were 50 and 46 Gy, respectively. The median cumulative biological equivalent doses (BED) were 200.4 (alpha/beta = 2 Gy) and 115.2 Gy (alpha/beta = 10 Gy). During follow-up, corticosteroid medication and the WHO-performance were registered at regular intervals. The radiological response was assessed by reviewing all available CT- and MRI-films. Potentially prognostic factors with respect to survival were evaluated by both univariate and multivariate analyses. RESULTS: A clinical response (i.e. clinical improvement) was seen in 24% of the patients. Of the evaluable patients, nearly one-third showed a complete (8%) or partial (22%) radiological response. The median overall survival (OS) and progression-free survival (PFS) after retreatment were 10.9 and 8.6 months, respectively. By multivariate analysis, four independent prognostic factors for survival were identified: (1), the WHO-score before retreatment (P = 0.002); (2), the length of the interval between treatments (P = 0.008); (3), the tumour histology; and (4), the response to initial treatment (P values, 0.04). The median survival times for patients with WHO-scores of 0-1 and > or = 2 were 14.0 and 7.4 months, respectively. Patients with oligodendrogliomas had a median OS of 27.5 months, whereas patients with astrocytomas had a median OS of 6.9 months after retreatment. Long-term complications of retreatment were seen in three patients, all of whom had a cumulative BED(2) of > 204 Gy (with alpha/beta = 2 Gy). The quality of life after retreatment, however, was well preserved in the majority of patients. They remained ambulant and capable of self-care until the time of progression which occurred after 8.6 months (median PFS). CONCLUSIONS: After an initial treatment with radiation up to tolerance levels of normal brain tissue, reirradiation of recurring primary brain tumours seems feasible. During the time until clinical progression, patients remained independent with a reasonable quality of life.

Pigmented spleens in C57BL mice.

Approximately 15% of our highly inbred C57BL/6 mice show a spleen with a pigmented cranial part. Microscopically, abundant aggregates of pigment granules are observed primarily scattered between cells of the red pulp. They give a positive reaction with Perls' Prussian blue and stain heavily with silver-methenamine. Most of the granules are stored in macrophages. In some cases a number of granules are surrounded by a membrane. This abnormality may be designated haemosiderosis. In the present study we demonstrate that it is not related to the consumption of iron within the range normally found in laboratory animal diets. This suggests a genetic origin, although confirmation would require further research. If so, comparison with human idiopathic haemochromatosis is tempting. However, contrary to the human condition, organs other than the spleen are not affected, with exception of the liver. This organ contains minor deposits of pigment granules. Nor do affected animals appear to show any ill effects. Nevertheless, it seems worthwhile to investigate whether this phenomenon in C57BL mice could serve as a model for the human disease provided that a practical criterium becomes available for detection in the intact animal.

Absence of an additional fibrotic response caused by oxygen in the lungs of rats after the intratracheal administration of bleomycin.

Bleomycin 0.4, 0.6, 1.0 or 3.5 mg/kg body weight was administered via the trachea in rats. After various time intervals some of the animals were exposed to 50% oxygen for either 4 or 24 h. The rats were then sacrificed at different times. Control rats remained untreated or received physiological saline. Lung histology was studied by light microscopy. In a number of rats the lung content of hydroxyproline was determined. Mild reactions, namely increases in pneumocytes type II and macrophages, oedema and prefibrotic alterations were observed after the instillation of bleomycin. The reactions were comparable to those observed after additional hyperoxia alone. Lung hydroxyproline concentration was not increased after bleomycin plus oxygen as compared with bleomycin alone. We conclude that no added toxicity is caused by 50% oxygen supplied for 4 or 24 h subsequent to doses of bleomycin that lead to mild pulmonary abnormalities in the absence of hyperoxia.

Pulmonary toxicity after treatment with bleomycin alone or in combination with hyperoxia. Studies in the rat.

Female Wistar rats (n = 11) received bleomycin 10 mg kg-1 i.p. three times weekly for 6 weeks. Four weeks later part of the group (n = 7) were exposed to 50% oxygen in air for 4 h; the others served as unexposed controls. A further control group (n = 5) received physiological saline i.p. and was not exposed to oxygen. One week after the hyperoxia treatment all animals were sacrificed and the lungs prepared for histological and biochemical determinations. Although the average body weight of the bleomycin-treated rats decreased significantly compared with the saline-treated controls, no significant alterations in lung histology were found in regard to the occurrence of oedema, fibrosis, and type II pneumocytes. Intra-alveolar macrophages were significantly increased. Subsequent hyperoxia did not lead to a more pronounced effect, except for macrophage accumulation. The activities of superoxide dismutase and glutathione peroxidase were not changed either after administration of bleomycin alone or after combination with hyperoxia. It is concluded that bleomycin i.p. in doses comparable to those encountered clinically, administered alone or combined with hyperoxia, does not result in pulmonary damage in female Wistar rats.

Ozone-induced elevation of creatine kinase activity in blood plasma of rats.

Rats exposed to three different low concentrations of ozone for 2 hr show alterations in blood plasma activity comparable to those previously observed in mice. The reactions are explained as compensatory, possibly being involved in the initial phase of adaptation development.

Activity changes of pulmonary macrophages after in vivo exposure to ozone as demonstrated by cell adherence.

Macrophages obtained by lavage from the lungs of rats exposed to 0.1 or 0.2 mg/m3 (0.05 or 0.10 ppm) ozone (O3) for 16 h show increased activity as measured in vitro by cell adherence to nylon fiber. A difference in adherence is noticed between macrophages occurring in first or second lung washings. The latter are less sensitive to ozone stimulation. At ozone doses higher than 0.2 mg/m3, the effect disappears and is even negative for second-washing macrophages after exposure of rats to 0.8 mg/m3 (0.4 ppm). The increased activity observed after exposure to the lower levels of O3 is explained as a defensive reaction of the organism. Failure to stimulate activity or a decrease of activity, observed at the higher O3 concentrations, may point to adverse events.

Early transient accumulation of methotrexate in the cerebrospinal fluid of rabbits after treatment with methotrexate and roentgen rays.

Concomitant application of intrathecal methotrexate (MTX) and cranial irradiation has been described as being able to cause brain abnormalities in patients with leukemia. In the investigation presented, rabbits were treated once weekly for 6 weeks with intraventricular MTX and irradiation. Cerebrospinal fluid (CSF) sampled at various time points after each treatment contained for the samples obtained 4 hours after treatment increasing amounts of MTX. This indicated a retardation in MTX clearance from the CSF. Such a retardation might contribute to the generation of brain abnormalities, although no data have as yet been obtained to prove this suggestion.

Non-effectivity of roentgen irradiation in an in vivo rapidly growing murine lymphosarcoma.

The survival time of mice bearing a rapidly growing murine lymphosarcoma (cell doubling time 9.6 h) is hardly influenced by roentgen irradiation with fractions of 2 Gy, not even if delivered according to superfractionated schedules. Growth kinetic measurements reveal an almost complete mitotic block 6 h after exposure, followed by a large overshoot in cell proliferative activity. The dose-response curve for in vivo irradiated cells has a D0 of 1.9 and lacks a shoulder. Hence, repair of sublethal damage must be of restricted significance. The extremely strong proliferative capability appears to lead to rapid repopulation of the tumour. Typically, surviving cells show a high content of RNA and protein.

Distinct enzymatic responses in mice exposed to a range of low doses of ozone.

Short-term exposure of mice to low O3 doses, as defined by the product of concentration and exposure time (ct), was observed to induce alterations in two enzyme systems: first, that leading to changes in hepatic reduced ascorbic acid (RAA) content, and second to changes in plasma creatine phosphokinase (CPK) activity. RAA alterations were noticed immediately, 30 min and 120 min after termination of the exposure period, whereas CPK showed alterations immediately and 15 min after termination of the exposure. Later determinations, i.e., 24 hr after O3 exposure for RAA and 30 min after 03 exposure for CPK, revealed no significant differences when compared to control animals. Although differences in sensitivity existed, the dose response curves for both systems were more or less similar, showing a short decrease for the initial very low O3 doses, followed by a profound rise and a gradual decrease to control levels for subsequent ct doses. Exceptions were the 30 min curve for RAA and the immediate curve for CPK in so far as that both showed an additional depression. Neither plasma histamine nor plasma lactic acid dehydrogenase (LDH3) were observed to be altered by the range of O3 doses employed. These findings were explained on the basis of adaptation of the organism to a potentially noxious O3 stimulus by enhanced metabolic processes: a weak stimulus leading to only a small adjustment, and stronger stimuli to elevated enzyme activity as well. With increasing doses of O3 this elevation in enzyme activity was found to be gradually diminished, possibly due to a steadily growing demand, leaving the overshoot becoming continually smaller until a balanced state is achieved.

Nonspecific hypersensitivity of the skin.

Hairless albino mice have been used to test the hypothesis of circulating mediators originating from extensive dermatitis, which might be responsible for 'false'-positive patch tests and non specific hypersensitivity. Two open patch tests with 2 or 3% phenol solution were placed on one flank at an interval of 10 days. 48 h before the second application, part of the mice received an intermediate 10% phenol solution on the opposite flank. The remaining animals served as controls. In general, intermediately treated animals showed a more pronounced reaction to the second patch test as compared to the first test, i.e., a larger granulocytic infiltrate, more extensive epithelial lesions and a elevated erythematous wall. In 6 of the 22 animals, the difference was very striking. In controls, only modest differences were observed. These findings favor the hypothesis that mediators of inflammation present in the circulation strengthen the effect of weak skin irritants.

Kinetics of cell proliferation in a rapidly growing murine lymphosarcoma.

The growth kinetics of a murine lymphosarcoma were investigated the spleen and liver of mice by means of quantitative flow-cytofluorometric DNA measurements in individual cells in combination with 3H-thymidine incorporation into the DNA. The amount of DNA in the S-phase cells was calculated from the resulting DNA histograms. From the 3H-thymidine incorporation, related to the amount of S-phase DNA, the relative changes in the duration of the S-phase during the growth of the lymphosarcoma were estimated. A marked prolongation of the duration of the S-phase was observed in the course of the growth of the lymphosarcoma. The disappearance of cells of higher ploidy normally found in the liver indicates the elimination of those normal cells in the course of the tumour growth.