WCCL Debate: How to Classify SPTCL

Off treatment, behavior as a primary criteria — it behaves like malignancy, it just keeps clonally expanding. You don’t die of a lymphoproliferative disorder without treatment; you die of malignancy without treatment.

Michael Girardi, MD, professor and vice chair of the Department of Dermatology at Yale School of Medicine, and Joan Guitart, MD, professor of dermatology and director of the Cutaneous Lymphoma Program at Northwestern University Feinberg School of Medicine, debated whether subcutaneous panniculitis-like T-cell lymphoma (SPTCL) should be classified as a lymphoma at all — a four-part exchange spanning diagnosis, biology, and bedside management.

At the 6th World Congress of Cutaneous Lymphoma (WCCL), Girardi and Guitart took opposite sides of a deliberately provocative question — and soon acknowledged how much they agree. Guitart’s position is that SPTCL, in its CD4-positive, alpha/beta form, is best understood not as a lymphoma but as a lymphoproliferative disorder (LPD): a clonal, often autoimmunity-associated process that responds durably to immune-modulatory therapy and, in his extensive referral experience, does not progress to metastatic disease.

Girardi’s counter is that the malignant “lens” must be retained: that SPTCL is a peripheral T-cell lymphoma whose clonal cells behave like a cancer, and that the safest framework respects its potential to turn aggressive.

In the first segment, the two map the terrain of disagreement. Guitart argues that much of the early literature describing SPTCL as aggressive was confounded by gamma/delta cases that have since been split off as a separate, genuinely aggressive entity, and that the alpha/beta cases lack lymphoma-defining mutations. Girardi draws the analogy to mycosis fungoides — often indolent early, but demanding respect because some patients eventually reveal their true colors — and lands on a position both return to throughout: in practice, they can both be right.

The middle segments move into biology. The debate turns on whether clonality and growth pattern amount to malignancy. Girardi notes that metastasis is not a defining feature of lymphoma — these cancers can grow, persist, and kill within their tissue of origin — and that the malignant T cells rimming adipocytes are simply behaving as clonal effector cells, much as mycosis fungoides homes to the epidermis. He resists labeling methotrexate, JAK inhibitors, and similar agents as mere immune modulators, framing them instead as T-cell–directed therapies used across early lymphomas.

Guitart holds that clonal growth does not by itself imply lymphoma — that LPDs, including reversible processes, can carry low-level driver mutations without crossing into malignancy. He points to a telling biological asymmetry: cyclosporine, which can accelerate mycosis fungoides, works well in SPTCL.

He situates SPTCL alongside conditions such as marginal zone lymphoma, large granular lymphocytic disorders, and monoclonal B-cell lymphocytosis, where the field has wrestled with the same “indolent-versus-malignant” line.

But they both agree the question should be settled by how the disease behaves off treatment, and that the determinant is not a critical mass of mutations but the interplay of those mutations with the host immune system.

For Girardi, the fact that untreated SPTCL keeps accumulating clonal cells — that patients ultimately succumb to malignant behavior rather than to an indolent disorder — keeps it on the malignant side of the line. Guitart counters that the same can be said of disorders now formally classified as LPDs, and that he expects the consensus bodies to move SPTCL in that direction, even as it currently remains a lymphoma in the WHO and ICC schemes.

What unites them is what matters most at the bedside. Both warn that the greatest danger is over-treatment: a patient with an indolent process steered toward multiagent chemotherapy, allogeneic transplant, or myeloablation by a clinician who sees the word “lymphoma” on a pathology report and reacts to the most aggressive entities the term evokes. Both advocate referral to clinicians experienced with the disease, early and appropriate immune-modulatory therapy, PET/CT to gauge the true extent of disease, and clear communication that most patients will do well — even, in Guitart’s experience, those with hemophagocytic lymphohistiocytosis.

As Guitart frames the conversation he has with patients: he does not believe they have a lymphoma, that they may develop one in the future, and that he is confident he can control the disease without chemotherapy.

The disagreement over the label, in the end, is less a clinical rift than a window into how the field decides what counts as cancer.