T-cell prolymphocytic leukemia (T-PLL) is a rare, mature T-cell neoplasm with a heterogeneous clinical course, but poor overall survival (OS). In 2018 the T-PLL International Study group (TPLL-ISG) set out to define standardized criteria for diagnosis, treatment indication, and evaluation of response. These criteria were published in Blood in 2019. They will facilitate the design and conduct of clinical trials in T-PLL, which are necessary for the approval of new therapeutics by healthcare authorities. In addition they will provide a useful resource for clinicians treating this rare disease.
In 2019 we also reviewed results from 174 T-PLL patients who were diagnosed or treated at RMH between 1989-2019. This data was presented at the ASH meeting in December 2019. Mean age at diagnosis was 61 years old (range 32-88) and M: F ratio was ~2:1 (113:61). At diagnosis the median white blood cell count was 74 x 109/L (range 10-918), median haemoglobin 126 g/L (range 59-175) and median platelet count 116 x 109/L (range 7-513). Sufficient immunophenotyping data was available for analysis in 135/174 patients. The results showed predictably high expression of CD2, CD3, CD5, CD7, CD52 and TCRαβ. CD25 was positive in 67/135 (50%) of cases, which is higher than the 18-35% seen in the current literature. CD4+/CD8- cases comprised 83/135 (61%) with CD4-/CD8+ 19/135 (14%), CD4+/CD8+ 32/135 (23%) and CD4-/CD8- 2/135 (2%). We analysed OS by decade of diagnosis covering 3 decades 1990-1999, 2000-2009 and 2010-2019. The median OS for the whole cohort was 20.6 months with median OS of 21 months, 23 months and 19 months for each decade respectively. There was no statistically significant difference between the curves by log-rank analysis.
Alemtuzumab was used in 116 patients, 69/116 (59%) receiving it as frontline treatment and 47/116 (41%) as salvage therapy. In 50/116 (43%) alemtuzumab was used as single agent, the remaining 66/116 (57%) receiving combination therapy, mostly pentostatin.
Mean time from diagnosis to receiving alemtuzumab was 6.8 months (range 0-53 months). Overall response rate (ORR) to alemtuzumab was 94/116 (81%) with complete remission (CR) 69/116 (59%), partial remission (PR) 25/116 (22%) and no response (NR) 20/116 (17%). Alemtuzumab produced better response rates when used as intravenous frontline therapy.
Allogeneic stem cell transplant (allo-SCT) was performed in 34 patients. Relapse rate post allo-SCT was 47%, non-relapse mortality 38% and transplant related mortality 29%. Although relapse rates are high post allo-SCT there is a small cohort of patients who are achieving long-term remission.
Our data shows that outcomes in T-PLL have remained unchanged since the first decade of alemtuzumab usage, with no improvement in OS in the last 20 years. Despite improvements in diagnostic techniques and supportive care median OS is static at approximately 20 months. Notably, in the last decade in particular, referrals to our centre have included a higher proportion of patients with relapsed or refractory disease and this may be contributing to the lack of improved survival in our cohort. Nevertheless, these results highlight the need for novel therapies in T-PLL. Given the rarity of T-PLL, international, multicentre, randomised trials such as the ibrutinib and venetoclax trial are needed to improve outcomes.