Pigment production in this case is diagnostic of the metastatic lesion, namely a metastatic melanoma. This sometimes creates a diagnostic dilemma. Secondary to malignancies elsewhere. Most common in carcinoma or as systemic involvement with lymphoma. Rare in sarcomas.
Tumors invade lymphatics and spread to the local draining lymph node.
Here, colonization occurs first underneath the capsule in the marginal sinus. Grossly, the lymph node may be of normal size or significantly enlarged. Depending upon the rate of growth of the tumor, there may be necrosis, cystic change or hemorrhage. In extreme cases, cross section may reveal a completely or partially necrotic node, with the center appearing as a white pus-like material. Microscopically, the tumor may be seen initially as small deposits of tumor resembling the primary tumor in the marginal sinus.