Case Report: Multiple radiotherapy courses for extensive recurrent cutaneous metastases from colorectal cancer.

We report the management of a 36-year-old man presenting with rapidly progressive and highly symptomatic cutaneous metastases (CMs) from metastatic colorectal cancer (mCRC). He was referred to palliative radiotherapy because of painful and pruritic skin lesions. His history included two synchronous colorectal adenocarcinomas. Comprehensive next-generation sequencing identified the rectosigmoid tumor as the metastatic source and revealed a pathogenic germline BRCA1 mutation, supporting a precision systemic strategy (olaparib plus pembrolizumab). CMs were the patient's dominant source of morbidity and progressively involved new skin sites; the patient therefore, received three sequential courses of helical tomotherapy (Radixact®), each delivering 30 Gy in 10 fractions to extended superficial volumes exceeding 50 cm. Each course treated adjacent fields with limited high-dose overlap. Deformable co-registration with the prior plans and cumulative-dose review confirmed that the high-dose overlap was limited, distinguishing this approach from re-irradiation. A posterior skin strip was consistently spared to preserve lymphatic drainage and reduce the risk of compartment toxicity. All three courses produced a very good partial response (VGPR) at six weeks, with toxicity limited to grade 1 dermatitis (no grade ≥2). Crucially, repeated irradiation maintained durable symptom control, avoided escalation of opioid analgesia for approximately six months, and allowed continuation of the same systemic regimen for nine months until lung progression. This case illustrates that iterative skin-directed radiotherapy can deliver safe, repeatable, high-quality palliation in extensive CMs.