Incorporation of pre-existing collagen bundles in primary cutaneous melanoma.

In a previous qualitative study it has been shown that the incorporation of pre-existing collagen bundles from the reticular dermis into the bulk of melanoma lesions metastatic to the skin indicates rapid systemic spread. In the present study the amount of pre-existing dermal collagen in the bulk of the melanoma lesions in 267 cases of primary melanoma of the skin with a Clark level of at least III was quantitatively assessed using automated image analysis based on RGB (red, green and blue) colour images of sections stained with haematoxylin and eosin. There was a weak correlation between the amount of pre-existing collagen and the Clark level and the Breslow index. With regard to prognosis, a large amount of pre-existing collagen (> 0.13 mm2 per index slide) was significantly associated with a particularly poor outcome (24-month survival rate: 71 +/- 17% compared with 96 +/- 2%; log rank test: P < 0.001). It is clear that a large amount of pre-existing collagen bundles occurring as a particular feature of tumour-stroma interaction indicates high metastatic capacity in primary malignant melanoma.