Mucin quantity on MRI and outcomes following total neoadjuvant therapy in patients with rectal cancer.

OBJECTIVES

To evaluate the relationship between mucin quantity on MRI and outcomes following total neoadjuvant therapy (TNT) in patients with rectal cancer.

MATERIALS AND METHODS

This retrospective, single-center study included patients with rectal adenocarcinoma who underwent TNT followed by surgery or non-operative management (NOM) from January 2018-December 2019. Two abdominal radiologists independently scored baseline and restaging MRIs for mucin quantity in the tumor or tumor bed, using two classifications: < 50% vs. ≥ 50% (similar to histological classification) and no mucin vs. any mucin. Statistical analysis was performed to determine if patient outcomes differed between tumors of different mucin quantities.

RESULTS

Among 189 patients, 114/189 (60%) male, 75/189 (40%) female), the median age at diagnosis was 57 years (IQR: 48-68). On baseline MRI, 29/189 (15%) patients had tumor containing any amount of mucin, and on restaging MRI, 27/189 (14%) patients had tumor containing any mucin. 103/189 (54%) underwent surgery after TNT, and 86/189 (46%) underwent NOM. 59/189 (31%) experienced local recurrence, distant recurrence, or local regrowth. There were no significant differences in the rate of pathologic complete response/sustained clinical complete response, time to local recurrence/local regrowth, time to distant recurrence, and disease-free survival between tumors of different mucin quantity, regardless of the timing and criteria for determining mucin quantity (< 50% vs. ≥ 50% mucin criteria, and no vs. any mucin criteria on baseline MRI, restaging MRI and on histopathology, respectively).

CONCLUSION

Mucin on restaging MRI should not rule out NOM or prompt more aggressive therapy in the absence of other high-risk features.

KEY POINTS

Question Is there a correlation in mucin content of tumor and patient outcomes in the setting of total neoadjuvant therapy followed by surgery or nonoperative management? Finding There were no prognostic differences between tumors of different mucin quantity in multiple outcomes, including local recurrence, local regrowth, recurrence, and disease-free survival. Clinical relevance Although prior studies have shown conflicting results, our findings suggest mucin content on MRI may not predict worse outcomes in rectal cancer patients treated with contemporary total neoadjuvant therapy, including those managed nonoperatively.