Impact of acellular mucin pools on survival in patients with complete pathological response to neoadjuvant treatment in rectal cancer

Background: Rarely, patients with pathological complete response (PCR) after neoadjuvant chemoradiotherapy demonstrate acellular mucin pools. The prognostic significance of this finding is controversial. The objective of this study was to determine impact of acellular mucin pools on disease free and overall survival in patients with complete pathological response to neoadjuvant chemoradiotherapy in rectal cancer. Methods: One hundred and seventy two patients received neoadjuvant chemoradiotherapy for rectal cancer and underwent surgery. Patients were divided into two groups based on presence of acellular mucin pools. Locoregional failures, distant failures and deaths were compared. Expected 5 year disease free and overall survival was calculated. Results: Median follow-up was 36(4-94) months. Complete pathological response was identified in 35(20.3%) patients. Of these, 12(34.2%) had acellular mucin pools in resected specimen. Majority of mucin negative tumors were moderately differentiated (78% vs 25%) (P = 0.005). Median overall survival for mucin positive and mucin negative tumors was 4(1.3-5.7) and 3.3(0.1-6.3) years respectively. Expected 5 year disease free and overall survival for mucin positive and mucin negative tumors was 73% and 89% (P = 0.1) and 75% and 87% (P = 0.4). Conclusion: Acellular mucin pools in rectal cancer following a PCR to neoadjuvant treatment do not impact survival.