Lymphatic invasion predicts sentinel lymph node metastasis and adverse outcome in primary cutaneous melanoma

Background Sentinel lymph node (SLN) metastasis is a powerful predictor of survival in primary cutaneous melanoma. Lymphatic invasion (LI) may correlate with increased risk of SLN metastasis. Intralymphatic metastases, often difficult to detect on hematoxylin and eosin (H&E) stained sections, are readily identified with dual immunohistochemistry for melanocytic and lymphatic markers. Methods We used dual S100/D240 immunohistochemistry to detect LI in 125 melanomas from patients who underwent SLN biopsy and correlated LI with melanoma staging parameters and disease status. Results Dual immunohistochemistry allowed for the identification of LI in 33 cases (26%), compared to only 2% on H&E stained sections. Melanomas with LI showed greater thickness, higher mitotic rate and more frequent ulceration. Eleven of 33 cases with LI (33%) and 10 of 92 cases without LI (11%) were associated with a positive SLN (P = .006). More patients without LI were disease‐free at last follow‐up (80%) than patients with LI (50%; P = .002); LI was significantly associated with decreased progression‐free survival. Conclusion The detection of LI is improved by dual immunohistochemistry and predicts SLN metastasis. The presence of LI may impact therapeutic planning in melanoma, such as the decision to perform a SLN biopsy.