Just a cutaneous (keratotic) horn?

A 70 year old woman attended a dermatologist with a lesion on the dorsum of her right hand (fig 1). It had appeared over eight weeks and was painless but unsightly. She reported good health and no history of warts. Fifteen years ago, she had lymphoma treated by chemotherapy; her last treatment (biological therapy) had finished seven years ago and she had been well since. She had holidayed in Australia for three months at a time over the last three years and more recently had driven frequently from northern England to the south coast while a close relative was ill. She said she was careful to use sunscreen.

The lesion had a red, firm base 2 × 1 cm and 3 mm with a cutaneous horn protruding another 5 mm.

She had cryocautery twice by her general practitioner which did not alter the lesion and so chose to attend a private dermatologist. The lesion was excised.

What is the most likely diagnosis?