Prognostic significance of depth of gross or microscopic perirectal fat invasion in T3 N0 M0 rectal cancers following sharp mesorectal excision and no adjuvant therapy

Background and aims. Although the standard of care for T3 and/or N1-2 rectal cancers includes adjuvant chemoradiation, it is unclear whether T3 N0 patients with limited microscopic perirectal fat invasion warrant further therapy. Our aim was to determine the prognostic significance of gross perirectal fat invasion, or depth of microscopic perirectal fat invasion, in T3 N0 rectal cancers following sharp mesorectal excision and no adjuvant therapy. Patients and methods. Utilizing a prospective database, the medical records of 108 patients who underwent a potentially curative resection for T3 N0 rectal cancer between June 1986 and December 1994 were analyzed. All pathological specimens were re-reviewed by a single pathologist, and extent of perirectal fat invasion was measured in millimeters. Patients who received either preoperative or postoperative adjuvant therapy were excluded. Results. Macroscopic perirectal fat invasion (T3 gross) was present in 49 cases, absent in 40 cases (T3 microscopic), and not reported in 19 cases. Rectal cancers were stratified by extent of measured perirectal fat invasion into 3 mm or less and more than 3 mm. Five-year overall and local recurrence rates for the entire group were 19% and 8%, respectively. The disease-free survival, disease-specific survival, and overall recurrence for rectal cancers with 3 mm or less invasion vs. more than 3 mm invasion, or T3 gross vs. T3 microscopic, were not statistically different. Conclusion. Our data suggest that the extent of gross, or microscopic perirectal fat invasion (defined as >3 or less than or equal to3 mm), determined in the resected specimen, does not predict outcome in select T3 N0 rectal cancers.