Expression of two morphologic parameters concerning tumor-stroma interaction in benign and malignant melanocytic skin lesions.

The importance of tumor-stroma interaction in many solid tumors of the skin has been demonstrated in recent years. Invasion and metastasis require multiple interactions of the tumor cells with the surrounding stroma. In malignant melanoma most studies concerning tumor-stroma interaction focus on the peritumoral infiltrate, whereas other aspects of tumor-stroma interactions have not been considered. We investigated two morphologic criteria of tumor-stroma interaction in melanocytic skin tumors. Simple infiltration into the surrounding dermis or subcutis without evident stromal reaction (DERMSIMPLE) and the existence of morphologically intact collagen bundles of the reticular dermis within the tumor bulk (PRECOLL) were examined in 373 benign common nevi, 239 dysplastic nevi, 322 Spitz nevi, 368 primary malignant melanomas, and 344 melanoma lesions metastatic to the skin. Our results showed that there is a highly significant difference in the expression of DERMSIMPLE and PRECOLL between benign and malignant melanocytic skin tumors. Concerning DERMSIMPLE, 13.3% of benign skin lesions compared with 28.2% of malignant lesions were positive for this feature; PRECOLL was found in 13.8% benign and 37.1% malignant lesions (chi-squared test; p = 0.0001 for both features). Furthermore, it could be demonstrated that simple infiltration into the surrounding stroma as well as the existence of morphologically intact collagen bundles of the reticular dermis within the tumor bulk increases with tumor progression; between primary malignant melanoma and melanoma metastatic to the skin, for example, there was a highly significant difference for DERMSIMPLE, as well as for PRECOLL (chi-squared test; p = 0.00001). These data indicate that morphologic aspects of tumor-stroma interactions in different benign and malignant melanocytic skin lesions may reflect biological behavior of tumor cells. The analysis of further aspects of tumor-stroma interaction and the relation to the patient's outcome may lead to the development of further prognostic parameters in malignant melanoma.