The Cancer Institute Hospital

The last decade has seen a sharp increase in the number of scientific publications describing physiological and pathological functions of extracellular vesicles (EVs), a collective term covering various subtypes of cell-released, membranous structures, called exosomes, microvesicles, microparticles, ectosomes, oncosomes, apoptotic bodies, and many other names. However, specific issues arise when working with these entities, whose size and amount often make them difficult to obtain as relatively pure preparations, and to characterize properly. The International Society for Extracellular Vesicles (ISEV) proposed Minimal Information for Studies of Extracellular Vesicles ("MISEV") guidelines for the field in 2014. We now update these "MISEV2014" guidelines based on evolution of the collective knowledge in the last four years. An important point to consider is that ascribing a specific function to EVs in general, or to subtypes of EVs, requires reporting of specific information beyond mere description of function in a crude, potentially contaminated, and heterogeneous preparation. For example, claims that exosomes are endowed with exquisite and specific activities remain difficult to support experimentally, given our still limited knowledge of their specific molecular machineries of biogenesis and release, as compared with other biophysically similar EVs. The MISEV2018 guidelines include tables and outlines of suggested protocols and steps to follow to document specific EV-associated functional activities. Finally, a checklist is provided with summaries of key points.

BACKGROUND: Advanced gastric cancer can respond to S-1, an oral fluoropyrimidine. We tested S-1 as adjuvant chemotherapy in patients with curatively resected gastric cancer. METHODS: Patients in Japan with stage II or III gastric cancer who underwent gastrectomy with extended (D2) lymph-node dissection were randomly assigned to undergo surgery followed by adjuvant therapy with S-1 or to undergo surgery only. In the S-1 group, administration of S-1 was started within 6 weeks after surgery and continued for 1 year. The treatment regimen consisted of 6-week cycles in which, in principle, 80 mg of oral S-1 per square meter of body-surface area per day was given for 4 weeks and no chemotherapy was given for the following 2 weeks. The primary end point was overall survival. RESULTS: We randomly assigned 529 patients to the S-1 group and 530 patients to the surgery-only group between October 2001 and December 2004. The trial was stopped on the recommendation of the independent data and safety monitoring committee, because the first interim analysis, performed 1 year after enrollment was completed, showed that the S-1 group had a higher rate of overall survival than the surgery-only group (P=0.002). Analysis of follow-up data showed that the 3-year overall survival rate was 80.1% in the S-1 group and 70.1% in the surgery-only group. The hazard ratio for death in the S-1 group, as compared with the surgery-only group, was 0.68 (95% confidence interval, 0.52 to 0.87; P=0.003). Adverse events of grade 3 or grade 4 (defined according to the Common Toxicity Criteria of the National Cancer Institute) that were relatively common in the S-1 group were anorexia (6.0%), nausea (3.7%), and diarrhea (3.1%). CONCLUSIONS: S-1 is an effective adjuvant treatment for East Asian patients who have undergone a D2 dissection for locally advanced gastric cancer. (ClinicalTrials.gov number, NCT00152217 [ClinicalTrials.gov].).

Japanese mortality due to colorectal cancer is on the rise, surpassing 49,000 in 2015. Many new treatment methods have been developed during recent decades. The Japanese Society for Cancer of the Colon and Rectum Guidelines 2016 for the treatment of colorectal cancer (JSCCR Guidelines 2016) were prepared to show standard treatment strategies for colorectal cancer, to eliminate disparities among institutions in terms of treatment, to eliminate unnecessary treatment and insufficient treatment, and to deepen mutual understanding between health-care professionals and patients by making these Guidelines available to the general public. These Guidelines were prepared by consensus reached by the JSCCR Guideline Committee, based on a careful review of the evidence retrieved by literature searches, and in view of the medical health insurance system and actual clinical practice settings in Japan. Therefore, these Guidelines can be used as a tool for treating colorectal cancer in actual clinical practice settings. More specifically, they can be used as a guide to obtaining informed consent from patients and choosing the method of treatment for each patient. As a result of the discussions held by the Guideline Committee, controversial issues were selected as Clinical Questions, and recommendations were made. Each recommendation is accompanied by a classification of the evidence and a classification of recommendation categories based on the consensus reached by the Guideline Committee members. Here we present the English version of the JSCCR Guidelines 2016.

Recent studies suggest that one or more genes on chromosome 5q21 are important for the development of colorectal cancers, particularly those associated with familial adenomatous polyposis (FAP). To facilitate the identification of genes from this locus, a portion of the region that is tightly linked to FAP was cloned. Six contiguous stretches of sequence (contigs) containing approximately 5.5 Mb of DNA were isolated. Subclones from these contigs were used to identify and position six genes, all of which were expressed in normal colonic mucosa. Two of these genes (APC and MCC) are likely to contribute to colorectal tumorigenesis. The MCC gene had previously been identified by virtue of its mutation in human colorectal tumors. The APC gene was identified in a contig initiated from the MCC gene and was found to encode an unusually large protein. These two closely spaced genes encode proteins predicted to contain coiled-coil regions. Both genes were also expressed in a wide variety of tissues. Further studies of MCC and APC and their potential interaction should prove useful for understanding colorectal neoplasia.

Advanced Breast Cancer (ABC) comprises both locally advanced (LABC) and metastatic breast cancer (MBC) [1]. Although treatable, MBC remains an incurable disease with a median overall survival of ∼2–3 years and a 5-year survival of only ∼25% [2–4]. Some more recent series seem to indicate an improvement in median overall survival [5, 6].

BACKGROUND: Trastuzumab deruxtecan (DS-8201) is an antibody-drug conjugate composed of an anti-HER2 (human epidermal growth factor receptor 2) antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor. In a phase 1 dose-finding study, a majority of the patients with advanced HER2-positive breast cancer had a response to trastuzumab deruxtecan (median response duration, 20.7 months). The efficacy of trastuzumab deruxtecan in patients with HER2-positive metastatic breast cancer previously treated with trastuzumab emtansine requires confirmation. METHODS: In this two-part, open-label, single-group, multicenter, phase 2 study, we evaluated trastuzumab deruxtecan in adults with pathologically documented HER2-positive metastatic breast cancer who had received previous treatment with trastuzumab emtansine. In the first part of the study, we evaluated three different doses of trastuzumab deruxtecan to establish a recommended dose; in the second part, we evaluated the efficacy and safety of the recommended dose. The primary end point was the objective response, according to independent central review. Key secondary end points were the disease-control rate, clinical-benefit rate, duration of response and progression-free survival, and safety. RESULTS: Overall, 184 patients who had undergone a median of six previous treatments received the recommended dose of trastuzumab deruxtecan (5.4 mg per kilogram of body weight). In the intention-to-treat analysis, a response to therapy was reported in 112 patients (60.9%; 95% confidence interval [CI], 53.4 to 68.0). The median duration of follow-up was 11.1 months (range, 0.7 to 19.9). The median response duration was 14.8 months (95% CI, 13.8 to 16.9), and the median duration of progression-free survival was 16.4 months (95% CI, 12.7 to not reached). During the study, the most common adverse events of grade 3 or higher were a decreased neutrophil count (in 20.7% of the patients), anemia (in 8.7%), and nausea (in 7.6%). On independent adjudication, the trial drug was associated with interstitial lung disease in 13.6% of the patients (grade 1 or 2, 10.9%; grade 3 or 4, 0.5%; and grade 5, 2.2%). CONCLUSIONS: Trastuzumab deruxtecan showed durable antitumor activity in a pretreated patient population with HER2-positive metastatic breast cancer. In addition to nausea and myelosuppression, interstitial lung disease was observed in a subgroup of patients and requires attention to pulmonary symptoms and careful monitoring. (Funded by Daiichi Sankyo and AstraZeneca; DESTINY-Breast01 ClinicalTrials.gov number, NCT03248492.).

Previous studies suggested that one or more genes on chromosome 5q21 are responsible for the inheritance of familial adenomatous polyposis (FAP) and Gardner's syndrome (GS), and contribute to tumor development in patients with noninherited forms of colorectal cancer. Two genes on 5q21 that are tightly linked to FAP (MCC and APC) were found to be somatically altered in tumors from sporadic colorectal cancer patients. One of the genes (APC) was also found to be altered by point mutation in the germ line of FAP and GS patients. These data suggest that more than one gene on chromosome 5q21 may contribute to colorectal neoplasia, and that mutations of the APC gene can cause both FAP and GS. The identification of these genes should aid in understanding the pathogenesis of colorectal neoplasia and in the diagnosis and counseling of patients with inherited predispositions to colorectal cancer.

Human retrovirus adult T-cell leukemia virus (ATLV) has been shown to be closely associated with human adult T-cell leukemia (ATL) [Yoshida, M., Miyoshi, I. & Hinuma, Y. (1982) Proc. Natl. Acad. Sci. USA 79, 2031-2035]. The provirus of ATLV integrated in DNA of leukemia T cells from a patient with ATL was molecularly cloned and the complete nucleotide sequence of 9,032 bases of the proviral genome was determined. The provirus DNA contains two long terminal repeats (LTRs) consisting of 755 bases, one at each end, which are flanked by a 6-base direct repeat of the cellular DNA sequence. The nucleotides in the LTR could be arranged into a unique secondary structure, which could explain transcriptional termination within the 3' LTR but not in the 5' LTR. The nucleotide sequence of the provirus contains three large open reading frames, which are capable of coding for proteins of 48,000, 99,000, and 54,000 daltons. The three open frames are in this order from the 5' end of the viral genome and the predicted 48,000-dalton polypeptide is a precursor of gag proteins, because it has an identical amino acid sequence to that of the NH2 terminus of human T-cell leukemia virus (HTLV) p24. The open frames coding for 99,000- and 54,000-dalton polypeptides are thought to be the pol and env genes, respectively. On the 3' side of these three open frames, the ATLV sequence has four smaller open frames in various phases; these frames may code for 10,000-, 11,000-, 12,000-, and 27,000-dalton polypeptides. Although one or some of these open frames could be the transforming gene of this virus, in preliminary analysis, DNA of this region has no homology with the normal human genome.

For the purpose of advanced breast cancer (ABC) guidelines, ABC comprises both inoperable locally advanced breast cancer (LABC) and metastatic breast cancer (MBC).1,2 Advanced/metastatic breast cancer remains a virtually incurable disease, with a median overall survival (OS) of about 3 years and a 5-year survival rate of around 25%,3,4 even in countries without major accessibility problems. Survival is strongly related to breast cancer subtype, with the major advances seen in human epidermal growth factor receptor 2 (HER2)-positive ABC.

We developed a novel promoter system, designated SR alpha, which is composed of the simian virus 40 (SV40) early promoter and the R segment and part of the U5 sequence (R-U5') of the long terminal repeat of human T-cell leukemia virus type 1. The R-U5' sequence stimulated chloramphenicol acetyltransferase (CAT) gene expression only when placed immediately downstream of the SV40 early promoter in the sense orientation. The SR alpha expression system was 1 or 2 orders of magnitude more active than the SV40 early promoter in a wide variety of cell types, including fibroblasts and lymphoid cells, and was capable of promoting a high level of expression of various lymphokine cDNAs. These features of the SR alpha promoter were incorporated into the pcD-cDNA expression cloning vector originally developed by Okayama and Berg.

BACKGROUND: Trastuzumab deruxtecan (DS-8201) is an antibody-drug conjugate consisting of an anti-HER2 (human epidermal growth factor receptor 2) antibody, a cleavable tetrapeptide-based linker, and a cytotoxic topoisomerase I inhibitor. The drug may have efficacy in patients with HER2-positive advanced gastric cancer. METHODS: In an open-label, randomized, phase 2 trial, we evaluated trastuzumab deruxtecan as compared with chemotherapy in patients with HER2-positive advanced gastric cancer. Patients with centrally confirmed HER2-positive gastric or gastroesophageal junction adenocarcinoma that had progressed while they were receiving at least two previous therapies, including trastuzumab, were randomly assigned in a 2:1 ratio to receive trastuzumab deruxtecan (6.4 mg per kilogram of body weight every 3 weeks) or physician's choice of chemotherapy. The primary end point was the objective response, according to independent central review. Secondary end points included overall survival, response duration, progression-free survival, confirmed response (response persisting ≥4 weeks), and safety. RESULTS: Of 187 treated patients, 125 received trastuzumab deruxtecan and 62 chemotherapy (55 received irinotecan and 7 paclitaxel). An objective response was reported in 51% of the patients in the trastuzumab deruxtecan group, as compared with 14% of those in the physician's choice group (P<0.001). Overall survival was longer with trastuzumab deruxtecan than with chemotherapy (median, 12.5 vs. 8.4 months; hazard ratio for death, 0.59; 95% confidence interval, 0.39 to 0.88; P = 0.01, which crossed the prespecified O'Brien-Fleming boundary [0.0202 on the basis of number of deaths]). The most common adverse events of grade 3 or higher were a decreased neutrophil count (in 51% of the trastuzumab deruxtecan group and 24% of the physician's choice group), anemia (38% and 23%, respectively), and decreased white-cell count (21% and 11%). A total of 12 patients had trastuzumab deruxtecan-related interstitial lung disease or pneumonitis (grade 1 or 2 in 9 patients and grade 3 or 4 in 3), as adjudicated by an independent committee. One drug-related death (due to pneumonia) was noted in the trastuzumab deruxtecan group; no drug-related deaths occurred in the physician's choice group. CONCLUSIONS: Therapy with trastuzumab deruxtecan led to significant improvements in response and overall survival, as compared with standard therapies, among patients with HER2-positive gastric cancer. Myelosuppression and interstitial lung disease were the notable toxic effects. (Funded by Daiichi Sankyo; DESTINY-Gastric01 ClinicalTrials.gov number, NCT03329690.).

Advanced Breast Cancer (ABC) comprises both locally advanced breast cancer (LABC) and metastatic breast cancer (MBC) [1]. Although treatable, MBC remains virtually an incurable disease with a median overall survival (OS) of ∼3years and a 5-year survival of only ∼25% [2, 3]. The MBC Decade Report [2] shows that progress has been slow in terms of improved outcomes, quality of life (QoL), awareness and information regarding ABC. More recently, some studies seem to indicate an improvement in OS, mostly due to advances in human epidermal growth factor receptor 2 (HER2)-positive ABC [4–6].

Occludin is an integral membrane protein with four transmembrane domains that is exclusively localized at tight junction (TJ) strands. Here, we describe the generation and analysis of mice carrying a null mutation in the occludin gene. Occludin -/- mice were born with no gross phenotype in the expected Mendelian ratios, but they showed significant postnatal growth retardation. Occludin -/- males produced no litters with wild-type females, whereas occludin -/- females produced litters normally when mated with wild-type males but did not suckle them. In occludin -/- mice, TJs themselves did not appear to be affected morphologically, and the barrier function of intestinal epithelium was normal as far as examined electrophysiologically. However, histological abnormalities were found in several tissues, i.e., chronic inflammation and hyperplasia of the gastric epithelium, calcification in the brain, testicular atrophy, loss of cytoplasmic granules in striated duct cells of the salivary gland, and thinning of the compact bone. These phenotypes suggested that the functions of TJs as well as occludin are more complex than previously supposed.

We examined somatic mutations of the adenomatous polyposis coli (APC) gene in 63 colorectal tumors (16 adenomas and 47 carcinomas) developed in familial adenomatous polyposis (FAP) and non-FAP patients. In addition to loss of heterozygosity (LOH) at the APC locus in 30 tumors, 43 other somatic mutations were detected. Twenty-one of them were point mutations; 16 nonsense and two missense mutations, and three occurred in introns at the splicing site. Twenty-two tumors had frameshift mutations due to deletion or insertion; nineteen of them were deletions of one to 31 bp and three were a 1-bp insertion. One tumor had a 1-bp deletion in an intron near the splicing site. Hence, 41 (95%) of 43 mutations resulted in truncation of the APC protein. Over 60% of the somatic mutations in the APC gene were clustered within a small region of exon 15, designated as MCR (mutation cluster region), which accounted for less than 10% of the coding region. Combining these data and the results of LOH, more than 80% of tumors (14 adenomas and 39 carcinomas) had at least one mutation in the APC gene, of which more than 60% (9 adenomas and 23 carcinomas) had two mutations. These results strongly suggest that somatic mutations of the APC gene are associated with development of a great majority of colorectal tumors.

BACKGROUND: Stereotactic irradiation (STI) has been actively performed using various methods to achieve better local control of Stage I nonsmall cell lung carcinoma (NSCLC) in Japan. The authors retrospectively evaluated results from a Japanese multiinstitutional study. METHODS: Patients with Stage I NSCLC (n = 245; median age, 76 years; T1N0M0, n = 155; T2N0M0, n = 90) were treated with hypofractionated high-dose STI in 13 institutions. Stereotactic three-dimensional treatment was performed using noncoplanar dynamic arcs or multiple static ports. A total dose of 18-75 gray (Gy) at the isocenter was administered in 1-22 fractions. The median calculated biologic effective dose (BED) was 108 Gy (range, 57-180 Gy). RESULTS: During follow-up (median, 24 months; range, 7-78 months), pulmonary complications of National Cancer Institute-Common Toxicity Criteria Grade > 2 were observed in only 6 patients (2.4%). Local progression occurred in 33 patients (14.5%), and the local recurrence rate was 8.1% for BED > or = 100 Gy compared with 26.4% for < 100 Gy (P < 0.05). The 3-year overall survival rate of medically operable patients was 88.4% for BED > or = 100 Gy compared with 69.4% for < 100 Gy (P < 0.05). CONCLUSIONS: Hypofractionated high-dose STI with BED < 150 Gy was feasible and beneficial for curative treatment of patients with Stage I NSCLC. For all treatment methods and schedules, local control and survival rates were better with BED > or = 100 Gy compared with < 100 Gy. Survival rates in selected patients (medically operable, BED > or = 100 Gy) were excellent, and were potentially comparable to those of surgery.

The genome of human T-cell leukemia virus (HTLV) was surveyed in fresh tumor cells of 163 patients with lymphoma and leukemia from the southwest part of Japan where adult T-cell leukemia (ATL) is endemic. Leukemic cells of all 88 cases of ATL tested so far were found to contain the provirus genome and also found to be monoclonal with respect to the integration site of provirus genome. In most cases of ATL, leukemic cells contained one or two copies of the complete HTLV provirus genome, and it was shown that the single species of HTLV with a fully determined sequence is typical in ATL. Some cases of T-cell malignancies, diagnosed as chronic lymphocytic leukemia or non-Hodgkin lymphoma, also had the provirus genome in their tumor cells, whereas some cases with the same diagnosis did not. No cases of other types of lymphoma or leukemia contained the provirus genome in their tumor cells. Monoclonal integration of the HTLV provirus genome in all primary tumor cells of ATL not only indicates that HTLV directly interacts with target cells, which become leukemic, and that integration of the provirus genome is a prerequisite for development of ATL and possibly other related diseases but also indicates that the virus is not associated with other types of lymphoma or leukemia.

PURPOSE: IMpower133 (ClinicalTrials.gov identifier: NCT02763579 ), a randomized, double-blind, phase I/III study, demonstrated that adding atezolizumab (anti-programmed death-ligand 1 [PD-L1]) to carboplatin plus etoposide (CP/ET) for first-line (1L) treatment of extensive-stage small-cell lung cancer (ES-SCLC) resulted in significant improvement in overall survival (OS) and progression-free survival (PFS) versus placebo plus CP/ET. Updated OS, disease progression patterns, safety, and exploratory biomarkers (PD-L1, blood-based tumor mutational burden [bTMB]) are reported. PATIENTS AND METHODS: Patients with untreated ES-SCLC were randomly assigned 1:1 to receive four 21-day cycles of CP (area under the curve 5 mg per mL/min intravenously [IV], day 1) plus ET (100 mg/m 2 IV, days 1-3) with atezolizumab (1,200 mg IV, day 1) or placebo, and then maintenance atezolizumab or placebo until unacceptable toxicity, disease progression, or loss of clinical benefit. Tumor specimens were collected; PD-L1 testing was not required for enrollment. The two primary end points, investigator-assessed PFS and OS, were statistically significant at the interim analysis. Updated OS and PFS and exploratory biomarker analyses were conducted. RESULTS: Patients received atezolizumab plus CP/ET (n = 201) or placebo plus CP/ET (n = 202). At the updated analysis, median follow-up for OS was 22.9 months; 302 deaths had occurred. Median OS was 12.3 and 10.3 months with atezolizumab plus CP/ET and placebo plus CP/ET, respectively (hazard ratio, 0.76; 95% CI, 0.60 to 0.95; descriptive P = .0154). At 18 months, 34.0% and 21.0% of patients were alive in atezolizumab plus CP/ET and placebo plus CP/ET arms, respectively. Patients derived benefit from the addition of atezolizumab, regardless of PD-L1 immunohistochemistry or bTMB status. CONCLUSION: Adding atezolizumab to CP/ET as 1L treatment for ES-SCLC continued to demonstrate improved OS and a tolerable safety profile at the updated analysis, confirming the regimen as a new standard of care. Exploratory analyses demonstrated treatment benefit independent of biomarker status.

PURPOSE: Trastuzumab deruxtecan (T-DXd, formerly DS-8201a) is a novel human epidermal growth factor receptor 2 (HER2)-targeted antibody drug conjugate (ADC) with a topoisomerase I inhibitor payload. A dose escalation and expansion phase I study evaluated the safety and activity of T-DXd in patients with advanced HER2-expressing/mutated solid tumors. Here, results for T-DXd at the recommended doses for expansion (RDE) in patients with HER2-low (immunohistochemistry [IHC] 1+ or IHC 2+/in situ hybridization-) breast cancer (ClinicalTrials.gov identifier: NCT02564900) are reported. PATIENTS AND METHODS: Eligible patients had advanced/metastatic HER2-low-expressing breast cancer refractory to standard therapies. The RDE of 5.4 or 6.4 mg/kg T-DXd were administered intravenously once every 3 weeks until withdrawal of consent, unacceptable toxicity, or progressive disease. Antitumor activity and safety were assessed. RESULTS: Between August 2016 and August 2018, 54 patients were enrolled and received ≥ 1 dose of T-DXd at the RDE. Patients were extensively pretreated (median, 7.5 prior therapies). The confirmed objective response rate by independent central review was 20/54 (37.0%; 95% CI, 24.3% to 51.3%) with median duration of response of 10.4 months (95% CI, 8.8 month to not evaluable). Most patients (53/54; 98.1%) experienced ≥ 1 treatment-emergent adverse event (TEAE; grade ≥ 3; 34/54; 63.0%). Common (≥ 5%) grade ≥ 3 TEAEs included decreases in neutrophil, platelet, and WBC counts; anemia; hypokalemia; AST increase; decreased appetite; and diarrhea. Three patients treated at 6.4 mg/kg suffered fatal events associated with T-DXd-induced interstitial lung disease (ILD)/pneumonitis as determined by an independent adjudication committee. CONCLUSION: The novel HER2-targeted ADC, T-DXd, demonstrated promising preliminary antitumor activity in patients with HER2-low breast cancer. Most toxicities were GI or hematologic in nature. ILD is an important identified risk and should be monitored closely and proactively managed.

Oncolytic virus therapy is perhaps the next major breakthrough in cancer treatment following the success in immunotherapy using immune checkpoint inhibitors. Oncolytic viruses are defined as genetically engineered or naturally occurring viruses that selectively replicate in and kill cancer cells without harming the normal tissues. T-Vec (talimogene laherparepvec), a second-generation oncolytic herpes simplex virus type 1 (HSV-1) armed with GM-CSF, was recently approved as the first oncolytic virus drug in the USA and Europe. The phase III trial proved that local intralesional injections with T-Vec in advanced malignant melanoma patients can not only suppress the growth of injected tumors but also act systemically and prolong overall survival. Other oncolytic viruses that are closing in on drug approval in North America and Europe include vaccinia virus JX-594 (pexastimogene devacirepvec) for hepatocellular carcinoma, GM-CSF-expressing adenovirus CG0070 for bladder cancer, and Reolysin (pelareorep), a wild-type variant of reovirus, for head and neck cancer. In Japan, a phase II clinical trial of G47∆, a third-generation oncolytic HSV-1, is ongoing in glioblastoma patients. G47∆ was recently designated as a "Sakigake" breakthrough therapy drug in Japan. This new system by the Japanese government should provide G47∆ with priority reviews and a fast-track drug approval by the regulatory authorities. Whereas numerous oncolytic viruses have been subjected to clinical trials, the common feature that is expected to play a major role in prolonging the survival of cancer patients is an induction of specific antitumor immunity in the course of tumor-specific viral replication. It appears that it will not be long before oncolytic virus therapy becomes a standard therapeutic option for all cancer patients.

Recent studies have suggested the existence of a tumor suppressor gene located at chromosome region 5q21. DNA probes from this region were used to study a panel of sporadic colorectal carcinomas. One of these probes, cosmid 5.71, detected a somatically rearranged restriction fragment in the DNA from a single tumor. Further analysis of the 5.71 cosmid revealed two regions that were highly conserved in rodent DNA. These sequences were used to identify a gene, MCC (mutated in colorectal cancer), which encodes an 829-amino acid protein with a short region of similarity to the G protein-coupled m3 muscarinic acetylcholine receptor. The rearrangement in the tumor disrupted the coding region of the MCC gene. Moreover, two colorectal tumors were found with somatically acquired point mutations in MCC that resulted in amino acid substitutions. MCC is thus a candidate for the putative colorectal tumor suppressor gene located at 5q21. Further studies will be required to determine whether the gene is mutated in other sporadic tumors or in the germ line of patients with an inherited predisposition to colonic tumorigenesis.