New CD56 positive and cytotoxic T-cell cutaneous lymphomas from the World Health Organisation

Primary cutaneous T-cell lymphoma of unspecified type with cytotoxic phenotype: clinicopathological analysis of 27 patients

The objective of our study was to investigate the clinicopathological features of the currently ill-defined subtype of primary cutaneous T-cell lymphoma of unspecified type (CTCLU) with a cytotoxic phenotype and no Epstein-Barr virus (EBV) association. A series of 27 patients with CTCLU (median age 49 years; range 25-87 years; 18 men) was reviewed. Performance status scores above 1 (7%), clinical stages above 2 (15%), B symptoms (26%), extracutaneous involvement (30%), and a fatal course within 1 year of diagnosis (19%) were observed infrequently. The International Prognostic Index was high or high to intermediate in 11%, and the Prognostic Index for Peripheral T-cell Lymphoma unspecified was above group 2 in 22%. Notably, the rates of spontaneous regression and T-cell receptor gene rearrangements by polymerase chain reaction analysis were seen in 26 and 17% of our cases, respectively. Histologically, 22 patients had subcutaneous involvement of whom eight showed a lethal clinical course, and five patients without subcutaneous involvement were all survivors. Immunophenotypical and morphological features allowed us to subclassify our cases according to the following four categories: (1) epidermotropic CD8+ T-cell lymphoma (n=5); (2) cutaneous gamma/delta T-cell lymphoma (n=8); (3) cutaneous alpha/beta pleomorphic T-cell lymphoma (n=8); and (4) cutaneous medium/large pleomorphic T-cell lymphoma, not otherwise specified (n=6). All four of these groups of lymphomas exhibited a relatively favorable clinical course compared to previous reports. However, epidermotropic CD8+ T-cell lymphoma appeared to be unique with a higher ratio (80%) of spontaneous regression, a lower ratio (40%) of subcutaneous involvement, and a more favorable clinical course than the other three subcategories.

CD56 staining in Merkel cell carcinoma and natural killer-cell lymphoma: magic bullet, diagnostic pitfall, or both?

BACKGROUND

Antibodies to CD56 label natural killer (NK) cell lymphomas and neuroendocrine tumors such as Merkel cell carcinoma (MCC). In MCC altered by crush artifact or obscured by lymphocytes, the histologic features coupled with CD56 positivity can lead to an erroneous impression of NK-cell lymphoma.

METHODS

Eighteen cases of MCC were stained for CD56, CK20, MNF116, and pankeratin. The results were compared to histologic features and CD56 staining pattern of three NK-cell lymphomas.

RESULTS

Three of 18 cases of MCC histologically resembled lymphoma, and CD56 positivity with CD3 and CD20 negativity initially raised the possibility of NK-cell lymphoma. Two additional cases were obscured by dense inflammation, again suggesting the diagnosis of lymphoma. Seventeen of 18 MCC labeled for CD56 and an equal number stained for CK20. All MCC tested were positive for CAM5.2 (14/14) and MNF116 (17/17). Antibodies to pankeratin labeled only one of 18 MCC. Staining for CD56 was stronger in MCC than NK-cell lymphomas.

CONCLUSIONS

CD56 is a sensitive marker for MCC as well as for NK-cell lymphoma, but is not specific. Importantly, CD56 positivity in crushed or inflamed biopsies of MCC may lead to an erroneous impression of NK lymphoma. Awareness of this potential pitfall will prevent misdiagnosis. McNiff JM, Cowper SE, Lazova R, Subtil A, Glusac EJ. CD56 staining in Merkel cell carcinoma and natural killer-cell lymphoma: Magic bullet, diagnostic pitfall, or both?