Other malignant tumours
Dermatofibrosarcoma protuberans is a slowly grow-ing malignant tumour of fibroblasts, arising usually on the upper trunk. At first it seems like a dermato-fibroma or keloid but, as it slowly expands, it turns into a plaque of red or bluish nodules with an irregular protuberant surface. It seldom metastasizes. It should be removed with extra wide margins, and even then will sometimes recur.
About 3% of patients with internal cancers have cutaneous metastases. They usually arise late and indicate a grave prognosis, but occasionally a solitary cutaneous metastasis is the first sign of the occurrence of a tumour.
The most common cutaneous metastases come from breast cancer. The skin of the breast is also most often involved by the direct extension of a tumour. This may show up as a sharply demarcated and firm area of erythema (carcinoma erysipeloides), firm telangiectatic plaques and papules (carcinoma telan-giectoides) or as skin like orange peel (peau d‚Äôorange) caused by blocked and dilatated lymphatics. Carcinoma of the breast may also send metastases to the scalp causing patches of alopecia (Fig. 18.61), or to other areas as firm and discrete dermal nodules.
Other common primaries metastasizing to the skin are tumours of the lung, gastrointestinal tract, uterus, prostate and kidney. The most frequent sites for sec-ondary deposits are the umbilicus and the scalp.