The impact of location on the prognosis of squamous cell carcinomas of the anorectal region

Background: Because anal and rectal squamous cell carcinomas (R-SCCs and A-SCCs) share a common histology and an excellent response to chemoradiation, we hypothesized that R-SCC and A-SCC may represent a similar biological entity, and location would not affect clinical presentation and prognosis. Methods: Patients diagnosed with R-SCC (n = 2881) and A-SCC (n = 21,854) were identified in the Surveillance, Epidemiology, and End Results database (1998-2013). R-SCCs were staged based on American Joint Committee on Cancer classification for A-SCC, and impact of location was analyzed accordingly. Results: Compared to A-SCC, R-SCCs were more common in females (65% versus 48%, P < 0.001) and older patients (62 versus 56 yrs, P < 0.001). R-SCC presented with more advanced disease than A-SCC: mean size 4.2 versus 3.6 cm; T4 14% versus 5%; nodal involvement 20% versus 15%; and metastases 13% versus 6% (all P < 0.001). In multivariable analysis, R-SCCs and A-SCCs had similar disease-specific survival (DSS) for stages 0, I, and III; however, stage II R-SCC had significantly worse DSS than A-SCCs (P = 0.002). This was due to a greater proportion of T3 (>5 cm) R-SCC tumors (36% versus 27%, P < 0.001), which had a lower DSS than T2 (2-5 cm) tumors. Within T3 and T4 tumors, R-SCCs had lower DSS than A-SCCs. Conclusions: R-SCC presented with higher stages than A-SCC, suggesting a delayed diagnosis. Larger R-SCC (T3-T4) had worse survival compared to T3-4 A-SCC, which may be due to a combination of more advanced disease within-stage as well as the use of less efficacious therapeutic regimens. Therefore, location may represent a significant prognostic factor for SCC of the anorectal region.