Clinical significance of acellular mucin in rectal adenocarcinoma patients with a pathologic complete response to preoperative chemoradiation

Objective: The objective of this study was to determine the prevalence and prognostic significance of acellular mucin within resected specimens of rectal cancer patients with a pCR following preoperative chemoradiation. Summary Background Data: The presence of acellular mucin pools in the resected specimens of patients with a complete response to preoperative chemoradiation is frequently reported as a marker of treatment effect. The clinical significance of the presence of acellular mucin with respect to local recurrence and survival outcomes is unknown. Methods: Data from a rectal cancer database was used to analyze 562 patients with nonmetastatic rectal adenocarcinoma treated between 1989 and 2004. The presence or absence of acellular mucin within the specimen was identified by the surgical pathology reports and confirmed by re-examination of H&E sections of surgical specimens. Results: Among the 562 patients, 100 patients (18%) had pCR. Acellular mucin was present in 27 (27%) of the 100 patients with pCR. The median follow-up interval was 87 months (range, 1-198 months). Local and distant failures occurred in 0 and 2 patients with acellular mucin, and in 1 and 6 patients without acellular mucin, respectively. The actuarial 7-year overall survival rates were 85% for patients with acellular mucin and 92% for patients without acellular mucin (P = 0.954). The actuarial 7-year disease-free survival rates were 81% and 87% (P = 0.764) and the 7-year freedom from relapse rates were 93% and 91% (P = 0.881) in patients with and without acellular mucin, respectively. Conclusions: Acellular mucin is present within 27% of resected specimens in rectal cancer patients with a pCR after preoperative chemoradiation. However, the presence of acellular mucin has no prognostic significance.