Reduced p16 expression correlates with lymphatic invasion in colorectal cancers

Background/Aims: P16, the tumor suppressor gene, plays a crucial role in the most important regulatory pathway involved in the G1/S transition, but its role in gastrointestinal neoplasia remains unclear. Methodology: To evaluate the possible p16 role in the development of colonic neoplasms, the authors studied p16 immunohistochemical expression of 84 lesions of colorectal cancers, 6 lesions of hyperplastic polyps, 59 lesions of adenomas and 8 lesions of carcinoma in adenoma. Immunohistochemical staining was processed by streptavidin biotin technique. The degree of expression pattern was classified into four types: absent, scattered, or nested, diffuse. Also, the correlation between immunohistochemical expression pattern and clinicopathological features was evaluated. Results: Compared with normal colonic mucosa, in which virtually no p16 expression was observed, p16 was overexpressed in hyperplastic polyps (33%: 2/6), adenomas (46%: 27/59), carcinoma in adenoma (88%: 7/8) and in adenocarcinomas (98%: 82/84). In colorectal cancers, when divided into positive (diffuse or nested) and negative (absent or scattered) subgroups, the negative group showed a higher ratio of lymphatic infiltration (p = 0.04), a higher ratio of deeper invasion (p < 0.01) and a higher ratio showing histology of mucinous carcinoma or poorly differentiated adenocarcinoma (p < 0.01). Conclusions: In colorectal cancers, a significant correlation of reduced p16 expression and lymphatic invasion was observed, which suggested that colorectal cancers with reduced p16 expression have more aggressive potential of lymphatic infiltration. Also a significant correlation between the overexpression of p16 and tumor progression was demonstrated.