Not all abdominal masses after colorectal cancer surgery are malignant: intra-abdominal fibromatosis masquerading as recurrence.

Aim: Intra-abdominal fibromatosis is an unusual mesenchymal tumour that can be locally aggressive without any metastatic potential. Fibromatosis may simulate cancer recurrence on imaging surveillance for colorectal cancer follow-up. The optimal treatment of recurrent peritoneal malignancy is cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC). Confirmatory biopsy of lesions suspicious for colorectal cancer recurrence may not be feasible, thereby rendering surgery the safest option. Our aim was to determine the incidence of fibromatosis in a cohort of patients undergoing CRS and HIPEC for suspected colorectal cancer recurrence.

Methods: One hundred and seventy-one CRS and HIPEC cases were performed at our Peritoneal Malignancy Institute between February 2007 and October 2018 for colorectal peritoneal metastases and were included in a prospectively maintained database.

Results: A total of 49 (29%) of 171 cases were performed for primary colorectal cancer with peritoneal metastases, whereas 122 (71%) of 171 cases were performed for suspected colorectal cancer recurrence detected on surveillance imaging after primary colorectal cancer resection. On histological analysis of the resected specimen, five (4.1%) of 122 cases undergoing CRS and HIPEC for colorectal recurrence had fibromatosis.

Conclusion: Fibromatosis can masquerade as colorectal cancer recurrence. In this series it occurred with an incidence of 4.1% among a cohort of patients undergoing CRS and HIPEC for probable recurrence. Surgical resection may be the only option to confirm the diagnosis and rule out malignancy.