Affiliation of authors: M. Frattini, D. Balestra (Department of Experimental Oncology and Unit of Experimental Molecular Pathology, Department of Pathology), S. Pilotti (Unit of Experimental Molecular Pathology, Department of Pathology), L. Bertario (Preventive and Predictive Medicine Unit), M. A. Pierotti (Department of Experimental Oncology), Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy.
Correspondence to: Marco A. Pierotti, Ph.D., Department of Experimental Oncology, Istituto Nazionale per lo Studio e la Cura dei Tumori, Via Venezian 1, 20133 Milan, Italy (e-mail: marco.pierotti{at}istitutotumori.mi.it).
Despite the potential effectiveness of colonoscopy and fecal occult blood tests in reducing colorectal cancer mortality, more specific, noninvasive tests are desirable. In this regard, it is possible to detect specific mutations of several genes in stool samples from colorectal cancer patients. Recently, the feasibility of a multitarget assay has been explored (1,2). Because the features of the mutations in the adenomatous polyposi coli (APC) and tumor protein 53 (TP53) make their study in stool difficult and time-consuming (2,3), efforts have focused on detecting the K-Ras gene, which often mutated in patients with colorectal cancer.
We analyzed 31 colorectal tumor samples by polymerase chain reactionrestriction fragment length polymorphism (PCRRFLP) and DNA sequencing and found 16 with K-Ras mutations. No associations were found between these mutations and clinicopathologic variables. To analyze K-Ras mutations in paired stool specimens from the same patients, DNA was extracted from both liquid and solid stool, checked for appropriate quality in PCR, and used in enriched-PCRRFLP analysis, which has a verified sensitivity of detecting one mutant out of 10 000 wild-type alleles (4). No K-Ras mutations were detected in fecal DNA from liquid stool samples. The same K-Ras mutation was detected in DNA from nine solid stool samples (9/14 = 62%) and in paired tumors (Table 1). Interestingly, mutations were detected in DNA from solid stool only when the paired tumor was located in the sigmoid colon or the rectum (four of four, and five of five, respectively). No K-Ras mutation was found in DNA from solid stool when the paired tumor was in the ascending colon (none of five; two-sided Fisher's exact test; P<.001). Our results are consistent with those recently reported (2), where no K-Ras mutations were found in stool samples from patients with tumors in the ascending colon, but K-Ras mutations were found in eight of 13 (61.5%) stool samples from patients with tumors located in the descending colon.
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In conclusion, our data suggest that the successful assessment of K-Ras mutations in stool mainly depends on tumor location. These results may explain why stool samples from patients with cancer in the ascending colon were negative, despite the presence of K-Ras mutations in the paired tumors. These conclusions may be relevant in the context of a stool screening approach for colorectal cancer.
NOTES
Supported by the Italian Association for Cancer Research (AIRC).
We thank Donata Penso for technical assistance in the sequencing analysis.
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