Analysis of the anatomic subsites, gender and age in unresectable advanced colorectal carcinomas in Tochigi, Japan suggests a shift in location towards the right side colon in elderly patients treated with cetuximab.

Colorectal cancer is a frequently occurring cancer whose incidence has shown a marked increase in recent years. Additionally, an increase in right side colon in elderly patients has been identified. Therefore, a clinicopathological study was conducted in 49 patients with unresectable advanced colorectal carcinomas to elucidate the association of clinicopathological characteristics and K-ras mutation. Of the 49 patients included in this study, 24 were aged <60 years with a male/female (M/F) ratio of 16/8 and 25 patients were aged ≥60 years with a M/F ratio of 16/9. Of the patients aged ≥65 years, 15 patients were enrolled as controls and the M/F ratio was 9/6. Results revealed that with regard to the subsite of cancer, unresectable advanced colorectal carcinomas developed in the right-sided colon in 13 patients, left-sided colon in 19 patients and rectum in 17 patients. Right-sided colon carcinomas were commonly identified in the elderly patients aged ≥65 years, with a marked tendency in the female patients (P=0.024). Immunostaining was performed for the epidermal growth factor receptor (EGFR) antibody in 40 patients to determine whether the K-ras gene would yield positive results. The mutant K-ras gene was identified in 8 patients (20%) and the frequency was lower compared with that of the normal colorectal carcinomas. Anti-EGFR antibody (cetuximab) is considered to be a molecularly targeted agent for unresectable advanced colorectal carcinomas. The increase in incidence of right-sided colon carcinomas as well as the increase in the number of patients presenting with colorectal carcinomas means this issue should be addressed. Sessile serrated adenoma/polyp (SSA/P) with b-raf mutation and CIMP (CpG island methylator phenotype) abnormality as a precursor lesion of right-sided colon carcinoma is common and since cetuximab refractory wild-type K-ras/mutant b-raf colorectal carcinoma may increase in elderly patients and patients with right-sided colon carcinoma, a simultaneous examination for the K-ras and b-raf gene abnormalities for the treatment of colorectal cancer using anti-EGFR antibody (cetuximab) is crucial. In addition, the multidisciplinary assessments regarding the effect of such treatments is likely to be determined based on cumulative results, such as the duration of patient survival.