Tandem Autologous Followed By Nonmyeloablative Allogeneic Transplantation in Relapsed High Risk Follicular Lymphoma Leads to Excellent Long Term Progression-Free Survival after 8 Years of Follow-up

Many new therapeutic agents have been approved for follicular lymphoma (FL) but none appear to be curative. Despite novel agents, some patients (pts) experience early relapse, become chemorefractory or suffer transformation into more aggressive lymphomas. Options for these pts are limited. High dose chemotherapy with autologous stem transplant (ASCT) prolongs progression free survival (PFS) and overall survival (OS) in FL pts in first relapse and registry data shows favorable outcome with ASCT in cases of histologic transformation. However, ASCT is usually not curative. Myeloablative allogeneic transplant (MT) has produced long term PFS but is hampered by significant non relapse mortality (NRM) while nonmyeloablative transplant (NMT) has a higher relapse rate compared to MT especially in high risk pts. Finally, many transplant studies have excluded these high risk pts such as those with chemorefractory or transformed disease.

We hypothesized that a tandem transplant consisting of an ASCT followed by a NMT would confer the same benefit as a MT without the associated high NRM by separating the high dose chemotherapy from graft versus host disease (GVHD) while preserving the graft versus lymphoma effect. The goal of our study was to improve long term PFS in high risk FL pts.

We therefore initiated a prospective protocol in April 2003, for pts with high risk relapsed FL as defined by chemorefractory disease, early 1^st relapse, >1^st relapse or transformation into aggressive histology. At least one therapy was attempted to document chemosensitivity prior to ASCT. However, regardless of disease status prior to transplant, pts underwent ASCT followed 3 months later by an outpatient NMT from an HLA-identical sibling. NMT comprised 5 days of fludarabine 30 mg/m²/day and cyclophosphamide 300mg/m²/day followed by an infusion of >2x10⁶CD34⁺ cells/kg. GVHD prophylaxis, chosen to take advantage of the low incidence of acute (a) GVHD and the putative protective effect of chronic (c) GVHD, consisted of tacrolimus starting on day (D) - 8 to achieve levels of 8-12 nmol/L then tapered off by D+100 or D+180 depending on disease risk and of mycophenolate mofetil 1g bid from D+2 to D+50. We previously reported on 27 pts with a follow-up (f/u) of 3 years (yrs). We now report a larger cohort of 40 pts with a median f/u of 8 yrs.

Up until July 2015, 40 pts were enrolled with a median age of 50 yrs (34-65). Pts had previously been treated with a median of 3 lines of therapy (2-6). Median time from diagnosis to ASCT was 33 months. Disease status at ASCT was: 14 CR, 16 PR and 10 refractory. Conditioning for ASCT included BEAM/BEAC (n=39), and Cy-TBI (n=1). In addition, 4 pts received radiotherapy after ASCT to sites of previously bulky disease. Median time between ASCT and NMT was 138 days (75-238). Pre NMT disease status was: 25 CR, 12 PR and 3 refractory.

Engraftment was prompt in all pts after ASCT and median neutrophil and platelet recovery were respectively 13 days (0-19) and 0 day (0-18) post NMT. Seven pts (18%) developed aGVHD: 2 grade II and 5 grade III. Overall, 29 pts (73%) developed cGVHD: 1 mild, 13 moderate and 15 severe according to NIH revised criteria. Median time to discontinuation of immunosuppression was 22 months. To date, 2 pts have progressed at 11 and 59 months post NMT (one died from relapse and one is now in CR after chemotherapy and DLI) and 5 pts died from either GVHD related complications (n=4) or unknown cause (n=1). All pts alive at last f/u were in CR. With a median f/u of 8 yrs in surviving pts (1-12), OS is 95% at 3 and 5 yrs and 82% at 8 yrs. PFS is 92% at 3yrs, 89% at 5 yrs and 80% at 8 yrs. NRM and relapse rate at 8 yrs are 18% and 6% respectively.

Based on our current results in 40 pts, we conclude that ASCT followed by sibling NMT for high risk relapsed FL is associated with excellent disease response and PFS. Furthermore, this tandem strategy appears to be safe and well tolerated. The incidence of cGVHD remains high but could in part explain the impressive PFS in this high risk cohort. This approach should now be further explored in a multi institution setting, include matched unrelated donors and consider the addition of rituximab post-transplant to reduce the incidence and severity of cGVHD with the hope that relapse will not be increased.

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