Histologic identification of malignant lymphoma cutis

Sections of 47 skin biopsies diagnosed during 1960-1970 as suggestive of or diagnostic of malignant lymphoma were retrospectively analyzed. Thirteen with monomorphous cutaneous infiltrates of reticulum cells or poorly differentiated lymphocytes were encountered; all were from patients who had extracutaneous manifestations of reticulum-cell sarcoma, poorly differentiated lymphosarcoma, or leukemia at the time of biopsy or within a year after biopsy. Diagnosis of well-differentiated lymphosarcoma or leukemia cutis is more tenuous, since mature lymphocytic infiltrates were encountered in patients with or without evidence of extracutaneous lymphoma. These are designated "unclassified" lymphocytic infiltrates of skin, requiring careful clinical exclusion of these types of malignant lymphoma. Other purported histopathologic discriminants of malignant lymphoma and pseudolymphoma, the latter term utilized to designate banal disorders characterized by a polymorphous infiltrate with or without atypical reticulum cells, are of little value for their distinction. These diagnostic criteria for malignant lymphoma cutis should clarify much of the pathologic and clinical uncertainty attendant upon the so-called "lymphoreticular" infiltrates of the skin.