Differential activation of total and EGF receptor (EGF-R) tyrosine kinase (tyr-k) in the rectal mucosa in patients with adenomatous polyps, ulcerative colitis and colon cancer.

BACKGROUND/AIMS: Tyrosine kinase and a number of growth factors, especially EGF and TGF-alpha are known to stimulate proliferation in much of the gastrointestinal tract, including colon. In humans increased colonic mucosal proliferative activity has been observed in numerous premalignant lesions including adenomatous polyps and ulcerative colitis. The aim of the present study was to determine the differences of proliferative patterns in patients with adenomatous polyps, ulcerative colitis and colonic adenocarcinoma as reflected by rectal mucosa tyrosine kinase, EGF receptor tyrosine kinase and PCNA and to evaluate the role of tyr-k in colonic mucosal cell proliferation during carcinogenic process.
MATERIALS AND METHODS: The study population comprised 40 patients, aged 17-74 years (mean 57), in which 10 patients had adenomatous polyps, 10-ulcerative colitis in remission phase, 10- colon adenocarcinoma and 10 healthy controls. After informed consent 6-8 rectal mucosal biopsy specimen were obtained at 10 cm from the anal verge at the beginning of the colonoscopy examination and at least 10 cm away from any macroscopic mucosal changes.
RESULTS: Mean PCNA labeling indices in patients with colon adenocarcinoma, adenomatous polyps, ulcerative colitis ulcerosa and healthy controls were respectively: 27.6% +/- 5.75; 12.18% +/- 6.76; 10.9% +/- 5.34 and 1.5% +/- 0.97. PCNA labeling index in rectal mucosa of patients with adenomatous polyps, ulcerative colitis and colon cancer was significantly higher (p < 0.01) than in the control group. An upward expansion of the proliferative compartment was also observed in patients with premalignant and malignant colon conditions as regards to the control group. Total tyrosine kinase activity in the rectal mucosa of patients with polyps was elevated by 219%, with ulcerative colitis by 224% and with colorectal carcinoma by 600% as regards to the control group. EGF receptor tyrosine kinase was increased in colonic mucosa by 35.2% in patients with adenomatous polyps, by 40.6% in patients with ulcerative colitis and by 123% in patients with colon cancer.
CONCLUSIONS: Increased values of this enzyme in the above mentioned group of patients may suggest that tyrosine phosphorylation represents an early sign of colonic mucosa susceptibility for cancer development. We conclude, that overall an EGF receptor-associated tyrosine kinase plays an important role in the development of hyperproliferative state of the colonic mucosa and colon carcinogenesis.