Primary extranodal soft tissue lymphoma of the extremities.

Since true primary lymphomas of soft tissues are extremely rare and there are few well-documented cases in the literature, we report eight cases to help define the clinical and pathologic features of this type of extranodal lymphoma. Among 7,000 malignant lymphomas seen at Mayo Clinic over a 10-year period, we found eight cases of Stage IAE extranodal malignant lymphoma that presented as a soft tissue mass in the upper or lower extremities. The tumors occurred in the following sites: thigh (n = 4), upper arm (n = 2), ankle (n = 1), and calf (n = 1). Two cases had low-grade histology: small lymphocytic lymphoma and follicular mixed small-cleaved and large-cell lymphoma. An intermediate-grade histology was present in two cases: diffuse mixed small- and large-cell lymphoma and diffuse large-cell (cleaved) lymphoma. Half of the patients had a high-grade lymphoma: diffuse large-cell (n = 3) and large-cell, immunoblastic (n = 1). The results of immunohistochemistry and electron microscopy in selected cases are discussed in the context of the differential diagnosis with other small, round-cell cancers. Four patients died of recurrent lymphoma, one at 7 months, two at 15 months, and one at 4 years. Three patients are alive without evidence of disease at 3, 8, and 13 years. One patient is alive and is receiving chemotherapy for locally recurrent lymphoma 6 months after diagnosis.