T-ALL presenting with i-TLP-like indolent clinical course with repeated spontaneous regressions.

Rapidly progressing ALL, a potentially fatal disease, demands timely diagnosis and treatment. On the other hand, spontaneous remission/regression (SR) is reported in various cancers including aggressive tumors like ALL. Infection or trauma-mediated immune system activation is assumed to cause SR, with the duration in cases of ALL typically being short. Indolent T-lymphoblastic proliferation (i-TLP) exhibits the uniform proliferation of TdT-positive T-cells, despite being a non-neoplastic disease, underscoring the significance of distinguishing it from T-cell acute lymphoblastic leukemia (T-ALL). i-TLP is expected to gain wider recognition and further advancements in understanding its pathology. Here, we present the case of a 59-year-old woman with T-ALL characterized by cycles of progression and SR followed by a rapid blast proliferation. This is the first reported case of T-ALL with repeated SR for more than one year, making this case an extremely rare clinical presentation. This challenging case will enhance comprehension of T-cell tumor pathogenesis.