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A Clone Is a Clone Is a Clone?

A finding of clonal proliferation does not necessarily indicate lymphoma.

The clinical significance of a clonal proliferation of T lymphocytes in the skin has gradually become less certain. At first, the laboratory data were promising: Clonality was identified in many cases of cutaneous T-cell lymphoma, suggesting that this finding could aid in early diagnosis. In recent years, however, the specificity of this finding has been called into question. Investigators found clonal populations of T cells in such wide-ranging conditions as lymphomatoid papulosis, pityriasis lichenoides, and lichen planus. In this study, the authors compared the T-cell populations in 13 biopsy samples from patients with histologically diagnosed pityriasis lichenoides chronica (PLC) and 14 samples from patients with histologically diagnosed pityriasis lichenoides et varioliformis acuta (PLEVA).

Monoclonal T-cell populations were found in 8 (57%) PLEVA cases and 1 (8%) PLC case. Interestingly, the single PLC case with a monoclonal T-cell infiltrate was first diagnosed as PLEVA on clinical examination. The authors conclude that PLEVA represents a benign monoclonal proliferation that arises from a subset of the polyclonal T lymphocytes in PLC lesions.

Comment: The authors' conclusion does not implicate PLC or PLEVA in the evolution of T-cell malignancy. Instead, the authors display a rare and admirable ability to analyze laboratory results in the context of an entire clinicopathologic setting. PLEVA rarely (if ever) progresses to overt lymphoma. Therefore, a finding of clonal proliferation does not necessarily imply such a progression. The hypothesis that PLEVA represents a preferential monoclonal evolution from polyclonal PLC is intriguing and requires additional follow-up. Stay tuned!

— Bruce R. Smoller, MD

Published in Journal Watch Dermatology September 9, 2002

Citation(s):

Weinberg JM et al. The clonal nature of pityriasis lichenoides. Arch Dermatol 2002 Aug; 138:1063-7.

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