Masquerading mucinous metastases: cutaneous colorectal cancer metastasis of the toes

Abstract

A 74-year-old female was admitted from the community with a 3-month history of a progressive, fungating lesion of the right great toe (Fig. 1). This lesion had been debrided previously and was thought to be a lymphangioma associated with chronic lymphoedema. The patient had no other symptoms on presentation, specifically no symptoms to suggest a primary malignancy. The case was referred on to medical oncology following biopsy on two separate occasions, which demonstrated tissue consistent with metastatic disease. Detailed histopathology showed cells with a polypoid mucosa covered in an atypical mucinous epithelium showing gastrointestinal differentiation, which stained positive for CK 20 and CDX and negative for CK7, S100, p63, PAX 8 and GCDFP-15 on immunohistochemistry. There was a focus of squamous epithelium within the sample consistent with the tissue of origin. A computed tomography and fluorodeoxyglucose positron emission tomography scan performed subsequently showed wide spread metastatic disease with pulmonary, bony, omental and nodal involvement. Avidity was also noted in the transverse colon. Colonoscopy revealed a sessile moderate-sized non-obstructing lesion at the splenic flexure and biopsy of this lesion revealed highly dysplastic tubular adenoma. Location of the lesion made biopsy technically difficult and it was the opinion of the operating surgeon that this lesion represented the primary malignancy. Following multidisciplinary team discussion of these findings, the toe lesion was therefore determined to represent a metastatic deposit of primary colorectal cancer. Following this diagnosis, there has been progression of the soft tissue lesion with disease involving the forefoot (Fig. 2). Given the widely metastatic disease, the patient was referred to radiation and medical oncology for further treatment. The patient has completed palliative targeted radiotherapy of the right foot and is planned for systemic therapy. The metastatic lesion is being managed in the community with dressings. The most common pattern of colorectal metastases is spread to the abdominal cavity, liver, lungs or bones. Unusual sites of metastatic disease are rare but reported throughout the literature. The metastatic spread of colorectal cancer to the skin has been described, and is usually reported in combination with advanced, widely metastatic disease and therefore usually carries a poor prognosis. The rate of cutaneous metastasis of colorectal metastases is