Peritoneal metastases from colorectal cancer managed by stereotactic body radiation therapy: presentation of a clinical case and review of literature.

Peritoneal metastasis (PM, or peritoneal carcinomatosis) is often associated with dismal prognosis. The treatment of peritoneal metastasis depends on several factors, including the type of primary cancer, the extent of metastasis and the patient's overall health condition. Apart from systemic chemotherapy and cytoreductive surgery (CRS), locoregional therapies such as hyperthermic intraperitoneal chemotherapy (HIPEC) or pressurized intraperitoneal aerosol chemotherapy (PIPAC) may improve tumour control. CRS is a complex procedure with high morbidity, performed only in approximately 25% of all eligible patients and the efficiency of other non-surgical therapies is not well known. The place of radiation therapy needs to be defined. A 62-year-old woman was referred for surgery for a few days' history of large bowel obstruction. A previous abdominopelvic CT showed an obstructive 3-cm mass in the proximal ascending colon, associated with small bowel dilatation. Right hemi-colectomy was performed. Work-up demonstrated on MRI (magnetic resonance imaging) sub-centimetric secondary liver lesions. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) ruled out other metastatic lesions. After multidisciplinary discussion, peri-operative systemic therapy based on FOLFOX-Bevacizumab was offered and was associated with stable disease for 7 months. Unfortunately, peritoneal progression was detected on PET/CT imaging. FOLFIRI-Bevacizumab was offered as second line systemic therapy followed by resection of residual masses. The patient was considered in remission for 5 months thereafter. A second isolated peritoneal relapse occurred involving the same 2 distinct sites. Second line chemotherapy was re-challenged. The oligorecurrent PM lesions were considered as non-operable. After multidisciplinary team discussion, stereotactic body radiation therapy (SBRT) was decided. The relapse sites were treated with 48 Gy, delivered in 6 fractions of 8 Gy given every other day. At the 22-month follow-up, the patient showed no signs of relapse on CT imaging and no treatment-related toxicities. Isolated peritoneal oligometastatic metastases are associated with poor prognosis. Cytoreductive surgery remains the historical standard of care treatment but represents a minority of all eligible patients. Our case and few other reports suggest that SBRT is a safe, reasonable, and non-invasive treatment option.