The correlation of regression in primary melanoma with sentinel lymph node status

Background: The significance of regression in primary melanoma has been disputed for many years. Some have suggested regression as a marker for poor prognosis while others have reported a negligible or even a favourable effect, on prognosis. Aim: To understand the significance of regression in melanoma and provide further information on whether patients should be subjected to sentinel lymph node biopsy (SLNB) on the basis of regression. Methods: 146 melanoma cases who had undergone SLNB were included in the study. The histological criteria for offering SLNB were melanoma > 1 mm in thickness, Clark's level IV or those with regression. Results: A statistically significant greater proportion of individuals without regression showed sentinel lymph node (SLN) positivity (p= 0.028) compared with those which do show regression. Metastatic disease correlated with growth phase of the primary lesion. All the node positive cases were in the vertical growth phase; none of the cases in radial growth phase and showing regression were associated with nodal metastasis (p= 0.029). 62 cases had melanomas with thickness < 1 mm and were in radial growth phase, yet were offered SLNB because of regression. Of these, 44 showed features of regression and all were node negative. The remaining 16 cases of thin melanomas did not show regression; 2 of these had sentinel node metastasis. Conclusion: Results suggest that regression is usually a favourable process, particularly in thin melanomas and that metastasis in '' thin melanomas showing regression '' is real but rare. Variant vertical growth phase, mitoses and other prognostically significant variables may be more important predictors of metastatic potential in thin melanomas.