Intraoperative radioimmunodetection.

The radioimmunoguided surgery (RIGS) system employs a monoclonal antibody (CC49), a radionuclide (Iodine-125), and a hand-held gamma-detecting probe (the Neoprobe model 1000). The prototype cancer studied has been colorectal cancer. The antibody identifies a type of mucin, the by-product of the adenocarcinoma cancer cell. The RIGS system localizes up to 90% of colorectal cancers and finds additional RIGS-positive tissues in >50% of the patients. More than 90% of the RIGS-positive visceral tumors are identified by routine hematoxylin-and-eosin (H&E) light microscopy, but the RIGS-positive lymph nodes are H&E occult tissues in >70% of the cases. Enhanced, more time-consuming methods have been developed to confirm hidden cancer cells in these lymph node tissues. Survival data confirm the importance of RIGS-positive tissues. RIGS-positive tissues remaining at the completion of the surgical procedure portend a much poorer outcome than if the patient is deemed RIGS-negative at the completion of the surgical procedure (i.e., all RIGS-positive tissue was removed at surgery).

Pharmacokinetics of iodine-125 CC49 monoclonal antibody in patients with colon cancer.

UNLABELLED: Radioimmunoguided Surgery techniques which use radiolabeled tumor specific markers and an intraoperative detector in an attempt to improve therapy and survival in patients with cancer have been under development for over fifteen years. Monoclonal antibody (MAb) CC49 is a second-generation murine IgG1 which has improved localization properties over its predecessor, MAb B72.3, and has been studied in a number of patients. In order to determine the pharmacokinetics of iodine-125 (125I) CC49 MAb, size-exclusion, high-performance liquid chromatography (HPLC) was used to assess radioactive components in serum and urine following administration of the drug to colon cancer patients. METHODS: Five patients received an intravenous infusion of 10 mg of MAb CC49 labeled with 2 mCi 125I. Following infusion, serum and urine specimens were collected from patients at predetermined time intervals prior to surgery. HPLC analysis of these specimens was completed to determine the radioactive species in each sample. RESULTS: Serum and urine specimens showed that serum levels of CC49 decrease exponentially and become unmeasurable by day 14 (half-life 1.89 days, +/- 0.19), with a steady, low-level of free 125I measurable in postinjection serum until day 21 after infusion. There was no evidence of MAb fragmentation or antibody:antigen (Ab:Ag) complex formation in serum, and no evidence of whole MAb, F(ab')2, or Fab fragment excretion in urine. Preinjection sera with MAb added in vitro also failed to demonstrate Ab:Ag complex formation. Analysis of urine showed low level excretion of free 125I which peaked by day 1 and declined exponentially through day 21, with a very low molecular weight (< 1 kDa) MAb fragment excreted in urine between 1 and 21 days. CONCLUSION: Radioiodinated 125I CC49 MAb remains in serum of cancer patients approximately 14 days, and tissue radioactivity beyond this time may reflect tissue sequestered MAb and/or free 125I and not "bloo pool" radioactivity. CC49 MAb appears to be deiodinated in small but significant quantities before it is metabolized, and clearance of radioactivity is mainly in free 125I form in urine. Measurable quantities of a < 1 Kda MAb fragment in urine and not serum may suggest a renal mechanism of MAb metabolism, but may also represent a metabolic end product of MAb metabolism with a very short serum half-life (T1/2) which accumulates in urine.

Surgical applications of gamma-detecting probes.

The RIGS system is a technology which was developed to provide a more sensitive and accurate method of detecting colorectal cancer during surgery. One of the components of this system is the hand-held, gamma-detecting probe [Neoprobe Model 1000instrument; Neoprobe Corporation, Dublin, Ohio), used by the surgeon to identify preadministered, radiolabeled monoclonal antibody which has localized to dis- eased tissue. RIGSuses sound-directed gamma detection to identify and locate cancer which may not be seen or felt by the surgeon. The success of RIGS has been largely due to the remarkable sensitivity of the gamma- detecting probe in detecting small amounts oflow-energy radioactivity. This attribute has led to the use of the probe for other surgical applications including pre- and intraoperative lymphatic mapping, and parathyroid localization. Surgery for melanoma, breast cancer, parathyroid disease, and colorectal cancer has been af- fected by the increased use of the gamma-detecting probe both in clinical trials and practice. This chapter will review the many applications of this new technology.

Radioimmunoguided surgery (RIGS) in recurrent colorectal cancer.

Since 1986, 191 patients with recurrent colorectal cancer have undergone surgical exploration 2 to 43 days after injection of 1.0 to 0.25 mg of monoclonal antibody (MAb) (B72.3 or 17-1A) radiolabeled with 5.0 to 1.0 mCi of 125I. The intraoperative use of a hand-held gamma detector (Neoprobe 1000) demonstrated that MAb identified tumor in 73% of cases. Clearer intraoperative definition of tumor margins and identification of occult tumor assisted the surgeon in the resection of liver metastases as well as nodal and pelvic disease. Unsuspected nodal disease was identified. The external use of the Neoprobe to scan the sacral region and intrarectal and intravaginal use led to the avoidance of operative procedures by defining inoperable disease. In approximately 25% of cases, the surgical procedure was modified based on Neoprobe findings. RIGS system provides a method of immediate intraoperative staging which may prevent additional recurrences, lead to earlier institution of adjuvant therapy, and result in improved survival.

Radioimmunoguided surgery in primary colon cancer.

Radioimmunoguided surgery (RIGS), the intraoperative use of a hand-held gamma detecting probe (GDP) to identify tissue containing radiolabeled monoclonal antibody (MAb), was performed upon 30 patients with primary colon carcinoma. Each patient received an intravenous injection of MAb B72.3 (1.0 to 0.25 mg) radiolabeled with 125I (5.0 to 1.0 mCi) 8 to 34 days before exploration. The GDP was used to measure radioactivity in colon tissue, tumor bed, nodal drainage areas, and areas of suspected metastases. Antibody localized to histologically documented tumor in 23 of 30 patients (77%). Tumor margins were more clearly defined in 20 of 30 patients (67%). GDP counts led to major alterations in surgical resection in five patients (17%) and changes in adjuvant therapy in four (14%). GDP counts identified occult liver metastases in two patients (7%) and correctly indicated the benign nature of liver masses in three (10%). In four patients (13%), occult nodal metastases were identified. RIGS can precisely delineate tumor margins, define the extent of nodal involvement, and localize occult tumor, providing a method of immediate intraoperative staging that may lessen recurrences and produce higher survival rates.

The impact of radioimmunoguided surgery (RIGS) on surgical decision-making in colorectal cancer.

Radioimmunoguided surgery (RIGS system) was performed in ten patients with rectal or low sigmoid colon carcinoma with the use of a hand-held gamma detector (Neoprobe 1000) intraoperatively and externally after injection of radiolabeled (125I) monoclonal antibody to detect pelvic and metastatic tumor. Fifteen procedures, including six exploratory laparotomies, four transperineal explorations, two transsacral explorations, one transvaginal biopsy, one brachytherapy, and one transanal polypectomy, were performed. Two patients had previous low anterior resection, seven abdominoperineal resection, and one a rectal polypectomy. Five patients had previous pelvic radiation therapy. Reoperation was indicated by elevated CEA levels in seven patients (70 percent), persistent pelvic pain in six (60 percent), and a suspicious radiologic study in seven (70 percent). RIGS system localized tumors verified by histopatholoy in all ten patients (100 percent); one patient with a positive CT scan and probe findings lacked histopathologic confirmation on frozen section, but had a tumor confirmed on permanent histology. Five major abdominal operations were avoided; in five patients major modifications were made in the surgical procedure based on probe findings. Six received chemotherapy or radiation therapy based on findings of the RIGS system. In six patients with negative or equivocal CT scans, the RIGS system localized histopathologically confirmed tumor. Major abdominal procedures can be avoided, the surgical approach modified, and other modes of therapy instituted earlier with the use of the RIGS system.

Radioimmunoguided surgery in recurrent colorectal cancer: the role of carcinoembryonic antigen, computerized tomography, and physical examination.

From January 1986 to December 1987, 32 patients with recurrent colorectal cancer had second-look radioimmunoguided surgery (RIGS system). All patients had pathologic confirmation of recurrence. The RIGS system identified 81% of recurrences, and in six patients recurrent tumor was identified only by RIGS. All patients had physical examination, carcinoembryonic antigen (CEA) assay, and computerized tomography of the abdomen and pelvis. Detection of recurrence was based on symptoms in six, elevated CEA value in 25, and physical examination in one. The CEA was elevated preoperatively in 30 patients; two false-negative results occurred in symptomatic patients who had pelvic recurrence. The median CEA value in those with liver recurrence was 30 ng/ml (range 5.2 to 298) and for pelvic recurrence 13 ng/ml (range 1.9 to 31) (P less than .05). The overall sensitivity of CT was 41% (abdomen other than liver 37%, liver 56%, and pelvis 22%). The combination of elevated CEA, symptoms, and physical findings identified 100% of recurrences. We conclude that a rising CEA remains the most accurate indicator of recurrence. CT should not be done routinely to detect recurrent colorectal cancer unless CEA is elevated or the patient is symptomatic. In our study the intraoperative use of the RIGS system aided the surgeon in identifying occult tumors.

The use of a hand-held gamma detector improves the safety of isolated limb perfusion.

We used two hand-held gamma-detecting probes (GDP) (Neoprobe 1000 system) capable of detecting small gamma emissions to monitor leakage in patients undergoing hyperthermic isolated limb perfusion (HILP) who received 800 microCi Technetium 99m pentetate through the perfusate. The percentage of gamma-ray leakage was calculated by a simultaneous reading of two probes at 1-minute intervals (one over the precordial area and one over the thigh) and this was compared to results of simultaneous blood sampling from the perfusate and systemic circulation at 15-minute intervals for gamma well counting (GWC). The percentage of leakage recorded by the GDPs was essentially identical to that detected by the GWC (7.3% and 8.2%, respectively at the conclusion of the perfusion). The GDP gives an immediate and accurate indication of the percentage of leakage during HILP, making it a safer procedure.

Staging of carcinoma of the breast using a hand-held gamma detecting probe and monoclonal antibody B72.3.

Radioimmunoguided Surgery (RIGS) uses a hand-held gamma detecting probe to identify radiolabeled monoclonal antibodies (Mab). Fourteen patients with carcinoma of the breast proved at biopsy received Mab B72.3 (5 millicuries of 125I per 1 milligram, Iodo-Gen method) intravenously six to 26 days before exploration. Probe counts were measured intraoperatively in mammary tissue and axillary lymph nodes. In the mammary tissue, the RIGS system identified tumor that was histologically confirmed in seven of eight patients and confirmed the absence in four of six patients. Probe counts were suspicious for tumor that was not proved histologically in two of 14 patients. Unsuspected tumor was identified in three of 14 patients. In axillary tissue, probe counts identified one of two tumors that were confirmed histologically and verified the absence of tumor in eight of 12 patients. Probe counts in axillary tissue were suspicious for tumor that could not be documented histologically in four of 14 patients. RIGS appears to be able to identify residual, subclinical and multicentric carcinoma of the breast and accurately delineate the pattern of antigenic drainage of tumor into adjacent lymph nodes.

Radioimmunoguided surgery using monoclonal antibody.

The potential proficiency of radioimmunoguided surgery in the intraoperative detection of tumors was assessed using labeled monoclonal antibody B72.3 in 66 patients with tissue-proved tumor. Monoclonal antibody B72.3 was injected 5 to 42 days preoperatively, and the hand-held gamma-detecting probe was used intraoperatively to detect the presence of tumor. Intraoperative probe counts of less than 20 every 2 seconds, or tumor-to-adjacent normal tissue ratios less than 2:1 were considered negative (system failure). Positive probe counts were detected in 5 of 6 patients with primary colon cancer (83 percent), in 31 of 39 patients with recurrent colon cancer (79 percent), in 4 of 5 patients with gastric cancer (80 percent), in 3 of 8 patients with breast cancer (37.5 percent), and in 4 of 8 patients with ovarian cancer (50 percent) undergoing second-look procedures. Additional patients in each group were scored as borderline positive. Overall, radioimmunoguided surgery using B72.3 identified tumors in 47 patients (71.2 percent), bordered on positive in 6 patients (9.1 percent), and failed to identify tumor in 13 patients (19.7 percent). Improved selection of patients for antigen-positive tumors, the use of higher affinity second-generation antibodies, alternate routes of antibody administration, alternate radionuclides, and more sophisticatedly bioengineered antibodies and antibody combinations should all lead to improvements in radioimmunoguided surgery.

Radioimmunoguided surgery using the monoclonal antibody B72.3 in colorectal tumors.

The authors have developed a hand-held gamma-detecting probe (GDP) for intraoperative use that improves the sensitivity of external radioimmunodetection. Radiolabeled monoclonal antibody (MAb) B72.3 was injected in six patients with primary colorectal cancer and 31 patients with recurrent colorectal cancer an average of 16 days preoperatively. The GDP localized the MAb B72.3 in 83 percent of sites. The technique, known as a radioimmunoguided surgery (RIGS) system did not alter the surgical procedure in patients with primary colorectal cancer but did alter the approach in 26 percent (8/31) of patients with recurrent colorectal cancer. Two patients avoided unnecessary liver resections and two underwent extraabdominal approaches to document their disease. The RIGS system may influence the short-term morbidity and mortality of surgery for colorectal cancer. Larger series and longer follow-up are needed to determine whether the RIGS system confers a survival advantage to the patient with colorectal cancer.

Radioimmunodetection of implanted tumors with gamma probe.

Tumor uptake of 125I- and 131I-radiolabeled anti-CEA antibodies was compared in female Swiss nude mice, each bearing a CEA-producing human colon adenocarcinoma xenografted in one flank. Counts from the tumor and contralateral flank were recorded with a manipulatable, cadmium-telluride crystal gamma detector at 24, 48, and 72 hours following injection. The animals were killed, and the tumors and other organs were removed, weighed, and then assessed in an automatic gamma counter. The cadmium-telluride counter was more efficient at counting 125I-labeled antibodies than 131I antibodies. The tumor to contralateral flank ratios improved with the use of a monoclonal anti-CEA and polyclonal anti-CEA in combination compared with the single antibodies. The investigation of the external counting characteristics of the portable gamma detector demonstrated the potential of the adjunctive use of intraoperative detection with external radioimmunoscintigraphy for detection and localization of gastrointestinal tumors.

Intraoperative probe-directed immunodetection using a monoclonal antibody.

To assess monoclonal antibody (MAb) 17-1A and its F(ab')2 fragment in intraoperative radioimmunodetection and to evaluate further the clinical usefulness of a hand-held gamma-detecting probe (GDP), we injected radiolabeled monoclonal antibody 17-1A three to six days preoperatively or its F(ab')2 fragment two to three days preoperatively into 18 patients with colorectal cancer. Intraoperative GDP counts with tumor-tissue ratios of 1.5:1 or greater were obtained from 15 (75%) of 20 tumor sites, with ratios averaging 2.3:1 for fragments and 3.4:1 for whole antibody. The GDP counts contributed to intraoperative decision making in three patients, either by localization of tumor not identified by inspection or palpation or by mapping margins of resection with histologic confirmation of a local/regional recurrence. These preliminary data demonstrate that probe-directed, intraoperative radioimmunodetection can assist the surgeon in detecting subclinical tumor deposits and thus better evaluate the extent of primary or recurrent colorectal cancers intraoperatively.

A gamma-detecting probe for radioimmune detection of CEA-producing tumors. Successful experimental use and clinical case report.

The detection of tumors with radiolabeled antibodies against CEA is possible; however, current nuclear medicine scanning cameras rarely detect tumors smaller than 2 cm in diameter. One of the limitations to tumor detection is the inability to place a detecting camera near a deeply seated intra-abdominal tumor. A hand-held gamma-detecting probe, suitable for intraoperative use, was designed to locate radioactive tumors. Experimental work with CEA-producing colon tumor xenografts in nude mice suggests this probe is more sensitive than external scanners in detecting small tumors. A case report documents the clinical use of this new intraoperative probe.

Portable gamma probe for radioimmune localization of experimental colon tumor xenografts.

Tumor radioimmune detection as presently practiced utilizes a gamma scintillation camera to image tumors. A major clinical limitation is the inability to detect tumors smaller than 2 cm. This limitation is due in part to the inverse square law which states: the number of detected radioactive counts is inversely proportional to the square of the distance separating a radioactive source from the detecting device. A hand-held gamma-detecting probe (GDP) suitable for intraoperative use has been developed. The GDP can be placed near radioactive tumors and take advantage of the inverse square law in a way not possible with external scanning cameras. The use of radiolabeled baboon carcinoembryonic antigen (CEA)-specific antisera produced increased tumor isotope localization in CEA-producing tumors compared to the injection of nonspecific antisera. Tumor isotope-antisera localization was not influenced by tumor volume or time since tumor implantation. The GDP probe counts demonstrated a high degree of correlation with gamma well tissue counts. The probe was able to detect preferential tumor localization in doses lower than could be detected with external scintillation cameras.