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World Journal of Surgery 9 1991 by the Soci6t~ lntcrnationale de Chirurgir

Monoclonal Antibodies in Imaging and Therapy of Colorectal Cancer Marianne K. Lange, M.D. and E d w a r d W. Martin, Jr., M.D. Department of Surgery, Ohio State University, Columbus, Ohio, U.S.A. Intraoperative detection of colorectal carcinoma with the Neoprobe gamma detector has been useful in surgical decisionmaking regarding resectability by localizing additional tumor not readily identified by palpation Or inspection, and in determining surgical resection margins. Tumor labeling has been achieved in 84% of the patients. Occult tumor has been identified in 18% of evaluable patients and changed operative decisions in 43 % of patients. New monoclonal antibodies with radiolabels offer hope for more effective agents for imaging, Radioimmunoguided Surgery | and potential therapeutic modalities.

Colorectal cancer is rising in incidence in the United States of America despite a greater awareness of the problem. Because of this, tumors are often detected at a later stage, may be inadequately treated and, consequently, recur 50% of the time. Recurrence usually manifests itself within 2 years after initial resection. Monoclonal antibodies (MAbs), predominantly mufine MAbs, have played a role both in colon cancer detection and therapy, primarily in recurrent colorectal cancer. Investigation of antibodies for clinical use began in the 1950's when Pressman [1] was exploring the concept of using polyclonal antibodies as carriers of isotopes to both malignant and normal tissues in the body. These antibodies would theoretically bind to tumor associated antigens. Pressman demonstrated that immune proteins could be used to successfully target radioactivity to tumors in living animals. But 25 years passed before any further work was carried out. In 1975, Nobel prize winners Kohler and Milstein [2] described and published the hybridoma technique which involves fusing spleen cells or other B-cells producing antibodies with highly proliferative myeloma cells. These resulting hybrids are screened for the presence of specific antibody and the positive ones are recloned and screened again. The positive subclones are then either frozen for future use or immediately grown up to amplify their antibody production. This technique opened the door for mass production of homogeneous antibodies of defined specificity, isotype or function. These hybrid cells combine two critical phenotypes from their progenitor cells: 1) the ability to secrete a specific antibody (from the B lymphocytes), and 2) the property of immortality (from the myeloma cell). Monoclonal antibodies have the advantage of recognizing a Reprint requests: Marianne K. Lange, M.D., 701 Ostrum Street, Suite 602, Bethlehem, Pennsylvania 18015, U.S.A.

single antigenic determinant in a complex mixture of antigens. They can be produced in great quantities in reproducible lots because the MAb is extracted from the same immortalized secreting clone. Large scale production can be achieved [3]. With the advent of the hybrid0ma technique, the hope was that tumor specific antigens could be identified, that is, antigens that were unique to tumor cells only. Rather, tumor associated antigens (TAA) have been identified which are found associated with malignant cells, but are usually not found solely on one particular type of cancer cell. Most often they are found on a family of cancers. For example, many adenocarcinomas, particularly those that have a similar differentiation pattern, may carry a certain TAA, but that TAA is not specific for adenocarcinoma of the colon. Another type of tumor associated antigen may be found in most squamous cell cancer or in tumors that secrete carcinoembryonic antigen (CEA). Unfortunately most of these TAA's also bind to certain normal tissues to some degree. The hope was that these MAbs were "magic bullets" and would bring new promise in cancer therapy. Although the initial high expectation for these "magic bullets" as single agent therapy for cancer was not fulfilled, MAbs have been extremely useful in cancer detection, cancer research, as an aid in pathological diagnosis and in diagnostic imaging. They have also shown some promise for therapy, particularly when used in combination with radioisotopes, toxins or chemotherapeutic agents. Additionally, MAbs have been used as assays to identify tumor antigens to screen for early diagnosis of cancer, to monitor therapy and to detect recurrence. Antigens which are excreted or shed by cancer cells can be detected in body fluids. MAbs have been used as tools to isolate and define specific tumor associated antigens and other naturally occurring molecules to which more specific MAbs can then be made [4-6]. In addition, this field of research is rapidly expanding and developing, initially with the development of MAb fragments (Fab' and F(ab')2), human monoclonal antibodies, and now with bioengineered chimeric MAbs and single chain fragments. Genes which code for antigens can be identified by MAbs and isolated by DNA transfection or cloned by recombinant DNA technology [7]. MAbs have played a major role in colorectal cancer diagnosis and therapy. Most of the monoclonal antibody work has involved murine monoclonal antibodies. Although a few human monoclonal

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antibodies have been made, the mouse has been the usual vehicle for MAb production. The problem faced in using routine monoclonals in the clinical setting, particularly when using the whole antibody, is the development of human anti-mouse antibodies (HAMA). In most of the murine MAbs examined clinically, 50% of injected patients develop HAMA following the second injection. Human anti-mouse antibodies can potentially cause an anaphylactic reaction but this is extremely uncommon. More importantly, HAMA causes the MAb to be excreted rapidly from the system. In addition to HAMA, another potential problem faced when using MAbs is that of tumor heterogeneity. A tumor cell population often contains a wide variety of cells expressing different antigens which prevents MAbs from completely coating all the cells as would be desired. A third problem is antigenic modulation which sometimes occurs between the primary and metastatic tumor [8]. MAbs potentially work by several mechanisms. Complement-mediated cytotoxicity is one means by which MAbs have an effect on target cells. The MAb invokes complement which sets off the complement cascade to mediate cell destruction. Complement-mediated cytotoxicity is primarily mediated by IgM MAbs [9]. A second means by which MAbs destro3, target cells is through the use of antibody dependent cellular cytotoxicity (ADCC). This usually involves IgG MAbs, in particular, IgG2a and IgG 3 [10-12]. Target cell destruction is accomplished by invoking killer cells, natural killer (N K) cells, macrophages, neutrophil s and even platelets. A third way that MAbs function is by the direct biological effects of MAb on target cells, e.g., by blocking cell proliferation. One such method involves use of monoclonal antibodies to growth factors and their receptors. All of these mechanisms rely on the antibody being intact, containing both the variable region and the Fc (or effector) region. Several human studies have been done looking at the effect of antibody alone on tumor killing, but responses were limited. Because MAbs which depend on ADCC or complement for tumoricidal activity do not appear to make a significant impact on large tumor volumes, monoclonal antibody conjugates have been developed. In these MAb conjugates, the MAb provides specificity which targets tumor while the conjugated toxin or isotope provides tumoricidal properties. Attachment of the conjugate must not alter the specificity of the MAb or change the function of the agent itself. The conjugate must not harm or only minimally harm normal tissues, but often, despite exhibiting acceptable specificity, the immunoconjugates cause considerable damage to normal tissues before excess unbound MAb conjugate is cleared from the system. Radioimmunoconjugates may be advantageous because they have a field effect, thus affecting more than the cell to which they bind. Work continues to create the ideal MAb or fragment which can overcome these current problems. Colorectal cancer has been an area of considerable focus in MAb research. Colorectal cancer is the most frequently studied tumor type using radiolabeled antibodies for radioimmunodetection (RAID). Colorectal cancer is the second most common cancer in men and women. There is no c0st-effective, reliable means of early detection. Because a number of antigens and MAbs associated with this tumor are available, it has been the subject of the majority of studies concerned with MAb targeting and imaging. Recurrent co!orectal cancer is associated with an elevated CEA level 80% of the time [13-15], making this antigen

World J. Surg. Vol. 15, No. 5, Sept./Oct. 1991

a focus of MAb production. Gold and Freedman [16] first described CEA in 1965 as a TAA which could serve as a target for radioactive antibodies. Since then, various anti-CEA MAbs have been developed including ZCE-025 [17], IMMU-4 (NP-4) [18], T84.66 [19] and A5B7 [20]. Other non-anti-CEA MAbs were developed which recognized other antigens. 17-1A is an IgGza that reacts with a cell surface protein expressed preferentially on human colorectal~ gastric and pancreatic carcinomas and, to a lesser degree, other human adenocarcinomas and normal tissues [21]. 17-1A has been extensively investigated in therapy as well as !maging trials [22, 23]. It was initially used in therapy trials utilizing ADCC. Another non-anti-CEA MAbs is 250-30.6, an IgGzu MAb which recognizes a secretory epithelial antigen [24]. B72.3, which has been extensively studied, recognizes TAG-72, a glyco-mucin antigen, tumor-associated-glycoprotein [25, 26]. Imaging Studies

Investigations have revolved around both imaging and therapy. Early studies were performed using planar imaging techniques. In 1973, Goldenberg [27] first imaged unconditioned golden hamsters growing human GW-39 colon xenografts. By labeling goat anti-CEA antibodies with 131I or 123I, he was able to show significant and selective localization of radiolabeled antibody in these tumors [28]. Reif [29] in 1974 and Mach [30] in 1978 carried out the first clinical trials of anti-CEA polyclonal antibodies in human subjects. These first trials were unsuccessful and they concluded that circulating CEA probably neutralized the radiolabeled antibody injected intravenously (i.v.). In September of 1977, Goldenberg [31] injected affinity-purified goat anti-CEA IgG labeled with 1311 into patients and demonstrated a focal lesion by planar imaging. The term RAID was coined for this imaging method. Because 1311 alone provides poor images, dual isotopes were used in a subtraction method which improved tumor images [32-34]. Goldenberg used a combination of 99mTc and 1311 for his dual isotope subtraction images. 123I was a good isotope used in earlier studies, but because it was unstable, expensive and had limited availability, it was not put into significant use. In 1980, Mach and colleagues [35] began investigating polyclonal antibody fragments in photoscanning. They felt there was a reduction in nonspecific accumulation of radioactivity in the liver~ however it did not significantly improve their detection rate. A significant improvement in imaging was noted when single photon emission computed tomography (SPECT) imaging was applied. Berche and coworkers [36] used SPECT in 17 patients injected with 1311 whole anti-CEA MAb and imaged 90% of the lesions. SPECT was capable of detecting much smaller tumor volumes (down to 2 cm 2) than planar imaging. Trials continued using 131I or 123I-labeled polyclonal and monoc!onal antibodies with 99mTC background subtraction. Planar and SPECT scanning were also compared to computed tomography. In 1986, Delaloye [37] administered Fab and F(ab')2 fragments labeled with 1231to 31 patients with colorectal cancer. Tumor sites were detected in 86% of the patients., The next aspect evaluated was antibody dosage. Most studies used 1 mg of antibody. A study done by Goldenberg [38] with the anti-CEA MAb NP-4 compared 1 mg and 10 mg dosages of MAb. They also compare d the Fab to F(ab')2 fragment and

M. Lange: Monoclonal Antibodies in Colorectai Carcinoma

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found essentially no significant difference between any of these of the patients in this group showed tumor localization not antibody reagents when labeled with 123I [39, 40]. detected by CT scans and other roentgenograms. Although 131I was the first radionuclide used for isotopeantibody cancer imaging [41], it is a suboptimal imaging isotope Intraoperative Radioimmunodetection Studies for several reasons. The gamma ray energy emitted by 1311 is not ideal for our conventional gamma cameras. Secondly, it B72.3 in conjunction with the Neoprobe | hand-held gamma gives significant beta emission [40] and thirdly, it dehalogenates detector has also been used for intraoperative detection at The very quickly [42]. Therefore, poor images are obtained using Ohio State University as well as in a larger multi-center trial [58]. In this trial patients with primary or suspected recurrent 131I. For this reason, other isotopes such as 111In and 99mTC are being investigated. Studies show that 111In is able to localize (based on a rising CEA) colorectal cancer underwent i.v. tumors well [43, 44], however it has the major disadvantage of injection with 2 mCi of 125I on 1 mg B72.3. High background accumulating in the liver making it virtually impossible to detect activity was allowed to dissipate over 2-4 weeks and patients liver metastases, a very common site of spread for colorectal were then taken to the operating room. Surgery was performed cancer [44]. If the lesions are at all detectable, they appear as while the hand-held gamma detector indicated whether tumor photopenic areas on the imaging scan. A large multicenter or otherwise suspicious tissue had taken up the antibodyItalian trial [45, 46] was carried out between 1985 and 1987 isotope complex. Tissues with an elevated level of activity were involving about 500 patients. An F(ab')2 fragment of an anti- then compared to normal tissue and the aorta and vena cava as CEA MAb was used. This trial investigated several variables background. Operative decisions were often made or changed including: I)131I vs. 111in labeling and 2) intravenous vs. intra- based on Neoprobe gamma detector findings. The multicenter peritoneal (i.p.) administration. The trial demonstrated that 131I trial indicated tumor labeling in 84% of the patients. Occult was a better tracer than 11qn. Imaging sensitivity was approx- tumor was identified in 18% of the evaluable patients and changes in operative decision making occurred in 43% of the imately 2 cm in diameter. Intraperitoneal injection appeared to patients. This intraoperative system has been useful in tailoring be superior to the i.v. injection with less nonspecific uptake and the surgeons' operative plans, e.g., foregoing a major resection a detection rate of 89% vs. 50%. Thus, this study as well as because of the detection of occult tumor elsewhere. It has others [47] showed that 111In-labeled MAb scanning is most further been helpful in defining surgical margins to govern the useful for imaging outside of the liver. Also, 11qn-labeled extent of resection. This method of tumor detection differs antibody accumulates in the colon, but this can be minimized by further from external imaging methods in that most of the the use of laxatives. external imaging studies have pertained to metastatic disease. Technetium-99m is a third isotope which has received a great The intraoperative use of the Neoprobe gamma detector in deal of attention as a label for MAbs. It would appear to have conjunction with radiolabeled MAb has been useful in deterideal imaging and chelating properties, however, its main short- mining the therapy for primary colon or rectal cancer as well. It coming is that it has a short half-life of only 6 hr. This is less of has been important in determining margins necessary to remove a problem with Mab fragments. However, studies we have done disease. It has detected unsuspected micrometastatic disease in on nude mice using several different fragments in conjunction mesocolic, peri-aortic, peri-portal or celiac axis lymph nodes at with the Neoprobe | gamma detector, a hand-held gamma the time of primary operation. These findings might change the detecting instrument, indicate that a minimum of 18 hr passes intraoperative strategy to include a wider mesenteric resection, before a 2:1 tumor to background ratio is achieved. At this a retroperitoneal or celiac axis lymph node dissection or sway point, the 99roTe has significantly decayed. Goldenberg and the surgeon to recommend postoperative chemotherapy. associates [48] completed a trial using the NP-4 Fab' fragment Overall, B72.3 is an adequate antibody in this system of labeled with 10-15 mCi of 99mWc.Tumor was imaged 98% of the Radioimmunoguided Surgery ~ (RIGS| However, other antitime with lesions in the range of 0.3-1.0 cm. bodies and fragments are being investigated to improve the Other antibodies used in clinical imaging studies include system's shortcomings: 1) length of time required for unbound MAbs against C A 19-9 [49, 50] and 17-1A [23, 49, 51, 52] (IgG MAb-isotope complex needed to clear the system, 2) inhomoand F(ab') 2 fragments), alone or in combination with an anti- geneous uptake of the MAb by the tumor cells, and 3) only CEA antibody given as a "cocktail". Additional imaging anti- 75-80% binding of MAb to tumors vs. a desirable 100%. We feel bodies include B72.3 [25, 53, 54], a colon-specific antigen-p that better antibodies and/or their fragments will improve the antibody, CSAp [55] and 791T/36 [56, 57] an anti-osteogenic problems with this system. cancer MAb. These have primarily been labeled with 131I. In general, all but B72.3 were poorer imaging antibodies than the Therapy anti-CEA antibodies [23, 51]. CA 19-9 and 17-1A as imaging agents could not detect lesions smaller than 3 cm and had a Monoclonal antibodies have been used therapeutically alone or sensitivity in the 50--60% range. A great deal of work has been conjugated to radioisotopes, toxins or chemotherapeutic done on B72.3 which is an anti-TAG-72 MAb originally devel- agents. CO17-1A, a membrane MAb developed at the Wistar oped against metastatic breast cancer. Imaging studies done on Institute, has been the most widely used MAb in colon cancer B72.3 labeled with either 131I or 111In indicated an overall therapy. It is cytotoxic to human colon cancer xenografts as detection rate of 80% in patients with recurrent colorectal well as in vitro studies [10, 12] which led to multiple human cancer [53]. In a second study involving patients with colorectal trials, including Phase I, Phase II and Phase III studies [21, or ovarian peritoneal metastases by Colcher and associates 59--61]. 17-1A acts through ADCC using an effector cell of the [25], 13q-labeled B72-3 was injected intraperitoneally and 30% macrophage/monocyte lineage. Efficacy reports have been vari-

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able, but no significant toxicity has been experienced in human subjects. Douillard and colleagues [2l] reported 6 trials in which a total of 8 patients exhibited a response, with 3 complete responses and 5 partial responses. A follow-up study done by LoBuglio and associates [62] showed 1 complete response and 4 stabilizations of disease when patients were given multiple large doses of 17-1A. They used 400 mg/wk for 1-4 weeks. An adjuvant trial for Dukes' B2 and C patients has begun, however, these results are not yet available. A trial combining 17-1A and interferon was carried out because interferon is known to stimulate monocyte ADCC as well as increasing NK cell activity. However, no responses were seen [63]. Recently a chimeric form of 17-1A combining mouse and human cells in 10 patients was carried out by LoBuglio and associates [64]. No HAMA response or toxicity was seen, but there was no evidence of tumor regression even after 6 weeks. Smith and associates [65] reported using a human-mouse heterohybridoma called 28A32 which is an IgM MAb recognizing a cell membrane and cytoplasmic antigen in colon cancer cells. Either 10 or 50 mg of MAb were injected weekly with no response reported. Because of the limited responses seen using MAb alone, immunoconjugates of various types have been constructed combining either toxins, chemotherapeutic agents, or radioisotopes with MAbs. The most common toxin used is the A chain of ricin, a ribosomal inhibitor protein produced from the beans of the plant Ricinus Communis [66]. Gallagher and Burk [67] coupled MAb to the A chain of ricin and demonstrated inhibition of protein synthesis in cultured human carcinoma cells. The immunotoxin XMMCO-791-RTA was shown to inhibit the growth of human tumor xenografts and was evaluated for the treatment of colorectal cancer. A Phase I trial by Byers and colleagues [68] showed reversible side effects with mixed tumor regression seen in 5 patients. Takahashi and associates [69] conjugated MAb A7 to either Mitomycin C or neocarzinostatin and had 3 patients demonstrate improvement of their liver metastases on CT scan as well as their clinical symptoms. While immunotoxins or chemo-immunoconjugates require internalization of the molecule for cellular cytotoxicity and hence affect only one cell, radioimmunoconjugates need only bind to the cell surface and advantageously cause a cytotoxic field effect. However, potential problems encountered with immunoisotopes for therapy are the length of time required to clear unbound MAb from the blood-pool-background and bone marrow toxicity. MAb fragments may potentially decrease these side effects. Many radioisotopes have been conjugated to anti-CEA and anti-TAG-72 MAbs. Most of these radioimmunoconjugates have been used as imaging agents. Stanley Order [70] has administered 1311and 9~ antiferritin to patients with primary hepatomas of the liver. While the 131I-antiferritin radioimmunoconjugate has caused some remissions in patients with primary biliary cancer, similar trials using 131I-anti-CEA have proved ineffective for colorectal cancer metastatic to the liver [71]. It is postulated that the neovasculature of metastatic disease is different than in primary hepatic cancer, making it difficult for the radioimmunoconjugate to reach tumor cells. Alternatively, the anti-CEA antibody used may not bind to tumor cells well or may have a shorter binding half-life preventing adequate long term binding to achieve cytotoxicity. Another MAb-isotope therapy study currently being carried out involves using 131I-labeled B72.3 given via the intraperitoneal route to

World J. Surg. Vol. 15, No. 5, Sept./Oct. 1991

patients with colorectal carcinomatosis. Results are not yet available. Summary

To date, both external and intraoperative imaging studies using radiolabeled MAbs have beert successful in localizing recurrent and/or primary colorectal tumors. External imaging studies have been useful in defining the location of cancer recurrence. Intraoperative detection, as with the Neoprobe gamma detector, has been useful in surgical decisionmaking regarding resectability, identifying additional tumor not readily identified by palpation or inspection, and determining surgical margins. New monoclonal antibodies with new radiolabels continue to be evaluated for imaging, RIGS, and potential therapeutic modalities. R6sum6

Grace aux anticorps monoclonaux marqurs et le d6tecteur gamma Nroprobe, on a 6valu6 la rrsecabilit6 et d6cel6 des formations tumorales non palpables ou drtermin6 les marges de srcurit6 aprrs r6section des cancers colorectaux chez 84% de nos patients. Une tumeur occulte a 6t6 identifire chez 18% des patients e t a fair changer l'attitude th6rapeutique chez 43% d'entre eux. L'utilisation des anticorps monoclonaux marqurs offre des espoirs nouveaux dans l'imagerie; la chirurgie radioguidre est une nouvelle voie de modalit6 thrrapeutique. Resumen

La exploraci6n intraoperatoria con instrumentos como el detector gamma Neoprobe ha sido de utilidad en el proceso de decisi6n quirfirgica en relaci6n a la resecabilidad, a la detecci6n de tumor adicional no fficilmente detectable mediante la palpaci6n y la inspecci6n, y e n la determinaci6n de los mfirgenes quirtirgicos. La identificaci6n del tumor ha sido posible en 84% de los pacientes. Tumor oculto ha sido detectado en 18% de los pacientes valorables y modific6 las decisiones quinirgicas en 43%. Los nuevos anticuerpos monoclonales radiomarcados ofrecen la esperanza de nuevas posibilidades para imagenologfa, cirugia radio-inmunodirigida y potenciales modalidades terapruticas. References

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M. Lange: Monoclonal Antibodies in Colorectal Carcinoma

monoclonal antibody to monitor the course of epithelial ovarian cancer. N. Engl. J. Med. 309:883, 1983 7. Morrison, S.L., Schlom, J.: Recombinant chimeric monoclonal antibodies. In Important Advances in Oncology, V.T. Devita Jr., S. Hellman S.A. Rosenberg, editors JB Lippincott, 1990, pp. 3-18. 8. Foon K.A.: Biological response modifiers: The new immunotherapy. Cancer Res. 49:1621, 1989 9. Neuberger, M.S., Rajewsky, K.: Activation of mouse complement by monoclonal mouse antibodies.. Ear. J. Immunol. 11:1012, 1981 10. Herlyn, D., Koprowski, H.: IgG2a monoclonal antibodies inhibit human tumor growth through interaction with effector cells. Proc. Natl. Acad. Sci. U.S.A. 79:4761, 1982 ll. Hellstrom, I., Brankovan, V., Hellstrom, K.E.: Strong antitnmor activities of IgG3 antibodies to a human melanoma-associated ganglioside. Proc. Natl. Acad. Sci. U.S.A. 82:1499, 1985 12. Herlyn, D., Herlyn, M., Steplewski, Z., Koprowski, H.: Monoclonal antibodies in cell-mediated cytotoxicity against human melanoma and colorectal carcinoma. Eur. J. Immunol. 9:657, 1979 13. Martin, E.W. Jr., Minton, J.P., Carey L.C.: CEA-directed secondlook surgery in the asymptomatic patient after primary resection for colorectal cancer. Ann. Surg. 202:310, 1985 14. Martin, E.W. Jr., Cooperman, M., King, G., Rinker, L., Carey, L.C., Minton, J.P.: A retrospective study of serial CEA determinations in the early detection of recurrent colorectal cancer. Am. J. Surg. 137:167, 1979 15. Martin, E.W. Jr., Cooperman, M., Carey, L C . , Minton J.P.: Sixty second-look procedures indicated primarily by rise in serial carcinoembryonic antigen. Surg. Reso 28:389, 1980 16. Gold, P., Freedman, S.O.: Specific carcinoembryonic antigens of the human digestive system. J. Exp. Med. 122:467, 1965 17. Abdel-Nabi, H.H., Schwartz, A.N., Hagino, C.S., Wahter, D.G., Unger, M.W.: Colorectal carcinoma: Detection with indium-Ill anticarcinoembryonic antigen monoclonal antibody ZCE-025. Radiology 164:617, 1987 18. Goldenberg, D.M., Gotdenberg~ H., Sharkey, R.M.: Imaging of colorectal carcinoma with radiolabeled antibodies. Semin. Nucl. Med. 19:262, 1989 19. Wagner, C., Yang, Y.H.J., Crawford, F.G., Shively, J.E.: Monoclonal antibodies for carcinoembryonic antigen and related antigens as a model system: A systematic approach for the determination of epitope specificities of monoclonal antibodies. J. lmmunol. 130: 2308, 1983 20. Blair, S.D., Theodorou, N.A., Begent, R.H.J., Dawson, D.M., Salmon, M., Riggs, S., Kelly, A., Boxer, G., Southall, P., Gregory, P.: Comparison of anti-foetal microvillus and anti-CEA antibodies in preoperative radioimmunolocalization of colorectal cancer. Br. J. Surg. (in press). 21. Douillard, J.Y., Lehur, P.A., Vignoud, J., Blotti'ere, H., Maurel, C., Thedrez, P., Kremer, M., Le Merel, B.: Monoclonal antibodies specific immunotherapy of gastrointestinal tumors. Hybridoma 5:S139, 1986 22. Mach, J.P., Chatal, J.F., Lumbroso, J.D., Buchegger, F., Forni, M., Ritschard, J., Berche, C., Douillard, J.Y., Carrel, S., Herlyn, M.: Tumor localization in patients by radiolabeled monoclonal antibodies against colon carcinoma. Cancer Res. 43:5593, 1983 23. Chatal, J.F., Saccavini, J.C., Fumoleau, P., Doulliard, J.Y., Curtet, C., Kremer, M., Le Merel, B., Koprowski, H.: Immunoscintigraphy of colon carcinoma. J. Nucl. Med. 25:307, 1984 24. Leyden, M.J., Thompson, C.H., Lichtenstein, M., Andrews, J.T., Sulfivan, J.R., Zalcberg, J.R., McKenzie, I.F.: Visualization of metastases from colon carcinoma using an iodine 131-radiolabeled monoclonal antibody. Cancer 57:1135, 1986 25. Colcher, D., Esteban, J.M., Carrasquillo, J.A., Sugarbaker, P., Reynolds, J.C., Bryant, G., Lawson, S.M., Schlom, J.: Quantitative analysis of selective radiolabeled monoclonal antibody localization in metastatic lesions of colorectal cancer patients. Cancer Res. 47:1185, 1987 26. Colcher, D., Esteban, J.M., Carrasquillo, J.A., Sugarbaker, P., Reynolds, J.C., Bryant, G., Lawson, S.M., Schlom, J.: Complementation of intracavitary and intravenous administration of MAb (B72.3) in patients with carcinoma. Cancer Res. 47:4218, 1987 27. Goldenberg, D.M., Witte, S. Elster, K.: GW-39: A new human

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