Abstract

Verrucous keratosis (VK) is a hyperkeratotic lesion that has been described in patients receiving BRAF inhibitor therapy, which has recently been approved for use in the treatment of BRAF-mutated colorectal carcinoma. Here, we describe an 85-year-old male with stage IV colon cancer who presented with multiple asymptomatic keratotic papules on his trunk and bilateral arms eight weeks after starting treatment with encorafenib and cetuximab. The differential diagnosis included viral warts secondary to immunosuppression, squamous cell carcinoma, and VK. A shave biopsy of the lesion on his shoulder demonstrated epidermal hyperplasia with papillomatosis, hyperkeratosis, and hypergranulosis. The findings were most consistent with VK. No squamous atypia was identified. The patient was instructed to continue his therapy while monitoring for signs of malignant transformation such as rapid growth of the lesions, pain, or erythema. At the two months’ follow up visit, the lesions appeared unchanged. Although encorafenib is generally an effective and well-tolerated drug, a range of cutaneous adverse effects have been reported. Notably, squamous cell carcinoma is seen in nearly 4% of patients. As BRAF inhibitor-associated VK may progress to squamous cell carcinoma, it is important to monitor these patients closely. With the increasing use of targeted therapies, dermatologists and dermatopathologists should be aware of the growing number of documented cutaneous manifestations and side effects associated with these regimens.

Financial Disclosure:
No current or relevant financial relationships exist.