Abstract Immunotherapy with programmed cell death 1 (PD‐1) checkpoint inhibitors combined with chemoradiotherapy shows great potential for cancer treatment and is getting extensively researched. However, a plethora of immune‐related adverse events (irAEs) has been observed during anti‐PD‐1 treatment, including cutaneous adverse events, such as vitiligo and pruritus. These adverse events may lead to treatment discontinuation. When anti‐PD‐1 treatment is combined with radiotherapy (RT), irAEs may be exacerbated. Here we present a case report of an elderly patient with stage IIIb rectal cancer, who developed PD‐1 inhibitor‐associated vitiligo. After a session of RT, vitiligo lesions enlarged shortly thereafter. After discontinuation of anti‐PD‐1 treatment, vitiligo lesions and pruritus quickly improved with appropriate treatment. The rectal cancer achieved clinical complete response with no sign of recurrence or metastasis during follow‐up. Considering the similar mechanism of anti‐PD‐1 treatment in targeting cancer and in inducing irAEs, cutaneous adverse events may be associated with favourable clinical response. Additionally, cutaneous irAEs aggravated by RT in this patient may suggested significant immune activation, which may occasionally contribute to tumour regression and favourable clinical outcome.
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