Note that the histology of the tumor resembles an infiltrating carcinoma of breast. Note as well that the tumor is close to the capsule of the lymph node. This is a common early site for implantation of metastatic tumors, since they enter the lymph node through afferent lymphatics which empty into the marginal sinus just below the capsule. Secondary to malignancies elsewhere, almost always carcinoma, or systemic involvement by lymphoma. Rare event for sarcoma.
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.