2816 - Comparative Outcomes of Radiation Therapy in Mycosis Fungoides and Primary Cutaneous CD4+ Small/Medium-Sized T-Cell Lymphoproliferative Disorder

Purpose/Objective(s): Radiation therapy (RT) is a key treatment modality for cutaneous T-cell lymphoproliferative disorders. Mycosis fungoides (MF) is an epidermotropic CD4+ T-cell lymphoma with an indolent, often multifocal course, whereas primary cutaneous CD4+ small/medium-sized T-cell lymphoproliferative disorder (PCSM-LPD) is a localized dermal CD4+ proliferation that most often presents as a solitary head and neck lesion. Despite widespread RT use in both conditions, outcomes have not been directly compared. This study compares complete response (CR) rates, remission durability, and relapse patterns after RT in PCSM-LPD versus MF.

Materials/Methods: A systematic literature search of PubMed, MEDLINE, and Web of Science through October 2025 identified studies reporting RT outcomes for MF or PCSM-LPD with data on CR, relapse, dose/fractionation, adverse events, or follow-up. Review articles, non-English publications, case reports with <4 patients, and studies without RT-specific outcomes were excluded. Primary endpoints were CR and relapse; secondary endpoints included progression-free survival (PFS), systemic progression, and adverse events.

Results: The search yielded 495 records; 25 studies were included, comprising 13 PCSM-LPD studies (n=452) and 12 MF studies (n=578). Median follow-up ranged from 13–44.5 months. In PCSM-LPD, CR rates ranged from 91–100%. Low-dose RT (4–8 Gy in 1–2 fractions) achieved CR rates comparable to higher-dose regimens. The largest series reported 100% freedom-from-progression at 3 years, with relapse in 11.6%, predominantly among patients with multifocal disease. No in-field relapses were reported; recurrences occurred exclusively at new cutaneous sites. No grade =2 adverse events were reported, with favorable cosmetic outcomes. Systemic progression was rare (0–2.4%). In contrast, MF outcomes were heterogeneous and stage dependent. Low-dose total skin electron beam therapy (TSEBT; 8–12 Gy) produced overall response rates of 85–99%, with lower CR rates (18–57%) and median PFS of 8–21 months; grade =3 toxicity was uncommon (5–7%). Higher-dose TSEBT (30–36 Gy) increased CR rates but did not proportionally prolong remission and was associated with greater fatigue and skin irritation. In early-stage MF, localized RT (8 Gy ×1) achieved 85% 5-year local control; however, relapses frequently occurred in untreated skin (median 12 months).

Conclusion: This systematic review provides a direct comparison of RT outcomes between MF and PCSM-LPD. In PCSM-LPD, RT achieves durable, treatment-free remission, supporting its role as definitive therapy. In MF, RT provides effective local control with potential for prolonged disease-free intervals in early-stage disease but typically necessitates ongoing management given frequent out-of-field relapse.