Familial adenomatous polyposis (FAP) is an autosomal dominant disorder and is the second most common genetic Colorectal cancer (CRC) syndrome, accounting for less than1%of all incidents CRC.CRC has been implicated as the most common cause of death in FAP patients, especially in those with coexisting CRC at initial diagnosis (FAP-CRC).The aim of this study was to compare the survival rate between Classic FAP and Attenuated FAP with coexisting CRC.

This was a retrospective cohort FAP study conducted in northwest Iran. From 2006 to 2016, 51 FAP-CRC individuals were selected from among 4588 CRC patients. Survival rates were calculated by Kaplan-Meier method and compared with log rank test.

The mean age at diagnosis of the primary CRC was 36 years (14 – 59) in the CFAP-CRC series versus 53.1(30- 70) years in AFAP- CRC group (P < 0.05). In CFAP_CRC group 76.5% had a left cancer location, vs. 64.7% in the AFAP cancer group. In the CFAP-CRC group 32.4% were end-stages cancer (TNM stage) vs. 17.6% in the AFAP-CRC group. The crude 5-years cumulative survival after the primary CRC was 46% in CFAP-CRC patients vs. 82% in AFAP-CRC patients (p = 0.01).

Our results show that overall survival of colorectal cancer in patients with AFAP is better than CFAP- CRC patients. This may be due to the different clinical pathological characteristics of neoplasia and to genetic alterations