Mucinous rectal cancers: clinical features and prognosis in a population-based cohort

Mucinous rectal cancers are generally associated with poor prognosis. This study aimed to clinically characterize mucinous rectal cancers in a defined region of Sweden.

All patients with rectal cancer in Uppsala and Dalarna, Sweden, between 2010 and 2018, were identified using the Swedish Colorectal Cancer Registry. Data were verified and updated by way of medical, radiology, and histopathology reports. Patients were selected if magnetic resonance imaging, biopsy, and/or surgical specimen were mucinous. Primary outcomes were overall survival (OS), time to recurrence (TTR), pattern of metastatization, and downstaging. Risk factors for recurrence were analysed with univariable and multivariable analyses.

Of 1220 patients with rectal cancer, 263 (22 per cent) had a mucinous specimen, median (interquartile range; i.q.r.) age was 71 (63-77) years, and 152 (58 per cent) were men. Most were localized in the low-middle rectum (76 per cent) and were stage III (53 per cent), or stage IV (28 per cent). The 5-year OS was 55 per cent (95 per cent c.i. 49 to 62); after total mesorectal excision (n = 164), 5-year OS was 75 per cent (95 per cent c.i. 68 to 83), and 5-year TTR was 68 per cent (95 per cent c.i. 60 to 77). In those with complete response (pCR), pStage I, pStage II, and pStage III, 5-year TTR was 93 per cent, 85 per cent, 74 per cent, and 44 per cent respectively. Synchronous metastasis was most common in the liver (64 per cent) and metachronous in the lungs (58 per cent). pCR was achieved in 14 patients, (13 per cent); whereas T and N category downstaging was achieved in 31 (28 per cent) and 67 patients (61 per cent) respectively. Perineural invasion had the strongest association with recurrence (hazard ratio 6.34, 95 per cent c.i. 2.50 to 16.10).

Mucinous rectal cancers have high recurrence rates, but pCR rate is more than 10 per cent. Perineural invasion is the main feature associated with recurrence.