[Do metachronous colorectal adenomas show proximal shift?]

To study the possibility of shift toward more proximal sites in colorectal cancer (CRC) after resection of tumors and synchronous lesions.

We reviewed 382 resected CRC diagnosed and followed-up with complete colonoscopies. The localization of metachronous adenomas was compared with that of synchronous lesions overall and by sex, tumoral size and the number of synchronous lesions. The frequency of exclusively proximal localization in first-, second- and third-generation metachronous adenomas was compared with that of synchronous adenomas.

A total of 54.5% of patients with CRC had synchronous adenomas. After a median follow-up of 48 months, with 2.74+/-1.47 colonoscopies/case, 42.4% developed metachronous adenomas, 16.8% second-generation adenomas and 7.3% third-generation lesions. Proximal shift was found in metachronous adenomas in both sexes, independently of tumoral size and the number of initial lesions. The frequency of exclusively proximal localization in adenomas was 21.2% in synchronous lesions, 39.5% in first-generation metachronous adenomas (p=0.0001; OR=2.46 [1.50-3.95]), 42.6% in second-generation metachronous adenomas (p=0.0008; OR=2.77 [1.44-5.31]) and 39.3% in third-generation metachronous lesions (p=0.0003; OR=2.41 [0.97-5.93]).

We found a high incidence of synchronous and metachronous adenomas. Metachronous adenomas showed a proximal shift, independently of sex, tumoral size and the number of synchronous lesions. This tendency was maintained in successive generations of metachronous adenomas, thus demonstrating the need to perform complete colonoscopies throughout the postoperative follow-up period.