A clinicopathologic study of 13 cases of primary lymphoma in soft tissue and review of literature.

Primary lymphoma in soft tissue is very rare. In order to understand the clinicopathological features of primary lymphoma in soft tissue, we found 13 cases (0.3%) of primary lymphoma in soft tissue by reviewing 4303 lymphomas diagnosed in our institution from 2010 to 2019. Tumors were found in the following sites: 8 in lower extremity (2 in leg, 1 in calf, 1 in knee and 4 in buttock), 1 in upper extremity (left shoulder) and 4 in the trunk (3 in waist and 1 in thoracolumbar). The most common histologic type was DLBCL (7/13, 54.8%). 6 cases of which had follow-up information. 25 patients were also selected by screening the English literature search (from Jan 2010 to December 2019) including 1102 studies. Compared to the results of literature review, our results are similar with them. The tumor sites were as follows: 10 in lower extremity, 4 in upper extremity, 9 in the trunk and 2 in masticatory muscle. The most common histological type was also DLBCL (n=11/25, 44%). Overall survival analysis of all 31 patients including our 6 cases with primary lymphoma in soft tissue showed no significant difference between different histological type (Log Rank P=0.120, Breslow P=0.157). The differential diagnosis includes malignant melanoma, rhabdomyosarcoma and metastatic carcinoma in soft tissue.