Current and upcoming treatment approaches to uncommon subtypes of PTCL (EATL, MEITL, SPTCL, and HSTCL)

Rare subtypes of peripheral T-cell lymphoma (PTCL) including enteropathy-associated T-cell lymphoma (EATL), monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL), subcutaneous panniculitis–like T-cell lymphoma (SPTCL), and hepatosplenic T-cell lymphoma (HSTCL) are underrepresented in most registries and clinical studies. Most of the literature is obtained from small case series, single-institution retrospective studies, and subgroup analyses of the largest studies with few recent and ongoing exceptions. Although the pathogenesis and biology of these entities have yet to be fully elucidated, global efforts by the scientific community have started to shed some light on the most frequently deregulated pathways. In this review, we highlight the most pertinent clinical and pathologic features of rare subtypes of PTCL including EATL/MEITL, SPTCL, and HSTCL. We also summarize the results of recent developments identifying potential targets for novel therapeutic strategies based on molecular studies. Finally, we highlight the underrepresentation of these rare subtypes in most clinical trials, making evidence–based therapeutic decisions extremely challenging.