Nail of a Hispanic female patient with onychomatricoma. This is a rare benign (non-cancerous) tumour of the nail matrix, the layer of cells at the base of a nail that the nail grows from. Changes to the matrix result in changes to the form and growth of the nail. The cause of onychomatricoma is unknown, but it is most common in caucasian women in their 50s. More than one finger or toe may be affected. Treatment is with surgical excision of the tumour. Recurrence is low.