Pilomatrixoma tumour. Light micrograph of a section through a tumour known as a pilomatrixoma or Malherbe's calcifying epithelioma. This benign tumour forms from epithelial cells and resembles a matrix of hair cells. The cells become calcified in a hard lump measuring between 3 and 30 millimetres in diameter. The lump is located in the dermis or in subcutaneous tissue. This condition is more common in childhood and in females. Treatment is by excision.