Dr Girardi on Properly Classifying SPTCL vs Lymphoma

At its worst, it looks like a malignancy, acts like a malignancy, and needs to be treated like a malignancy, and as such it should stay firmly in the malignancy category. We shouldn’t categorize something based on how it behaves on treatment, but how it behaves off of treatment.

Subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is rare even among the cutaneous T-cell lymphomas, presents deep in the fat rather than on the skin surface, and can look indistinguishable from a benign inflammatory process. This combination has made it one of the field’s genuine classification puzzles.

Michael Girardi, MD, professor and vice chair of the Department of Dermatology at Yale School of Medicine in New Haven, Connecticut, argued that despite that ambiguity, SPTCL belongs firmly in the malignancy category — a position he grounds in how the disease behaves off treatment rather than on it.

Speaking at the 6th World Congress of Cutaneous Lymphoma (WCCL), Girardi addressed whether SPTCL should be classified as a lymphoma at all and walked through why the entity is so easily mistaken in both directions.

The recognition problem starts with how SPTCL presents. Because the disease sits in the subcutaneous fat as nodules that are often felt before they are seen, it lacks the obvious surface findings of other cutaneous lymphomas; Girardi noted that PET/CT imaging is frequently a necessary step to gauge how much disease is actually present. Histology can help, but the defining features — a CD8-positive cytotoxic phenotype and the characteristic rimming of adipocytes by malignant T cells — may take time and clinical evolution to declare themselves.

The harder problem is the overlap with benign disease. Inflammatory panniculitides such as lupus panniculitis can look nearly identical clinically, on imaging, and at first pass histologically. Girardi emphasized that the two are not always mutually exclusive; some patients genuinely carry features of both. He described a “dual lens” early in the course: is the process sorting itself out as an inflammatory, autoimmune one, or as a malignant one? Cases that melt away with prednisone or methotrexate can look more like an immunologic condition than an oncologic one.

That is precisely where the classification stakes lie. The danger, Girardi explained, is assuming a definitive category too early — getting comfortable with a diagnosis that later proves wrong in either direction. He cautioned against anchoring on treatment response, since a response to immunosuppression does not by itself establish that a process is benign.

His resolution is to judge the disease by its off-treatment behavior. In a meaningful subset of cases, Girardi noted the process continues to progress off therapy, with clonal expansion, accumulating T cells, and emerging evidence of oncologic genetic drivers. These are features that Girardi argued keep SPTCL on the malignant side of the line, even as he acknowledged more data are needed.