Low-dose radiation therapy – with or without concurrent chemotherapy – appears promising as a treatment for patients with relapsed or refractory mantle cell lymphoma (MCL) or at least a bridge to subsequent therapy, according to findings published in Blood Advances.
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Mantle cell lymphoma
Matthew S. Ning, MD, of the department of radiation oncology at the University of Texas MD Anderson Cancer Center, Houston, and colleagues, said this is the first study to evaluate low-dose radiation therapy (LDRT) with chemotherapy as a treatment modality outside of palliative care for relapsed, multiple refractory MCL patients.
“Our findings indicate that LDRT imparts excellent [local control], minimal toxicity, and favorable outcomes in this setting,” the researchers said.
The study included 19 patients with a total of 98 sites of relapsed, refractory MCL who were treated from 2014 to 2018. The median follow-up was 51.3 months from initial diagnosis and 15.4 months from initial treatment with low-dose radiation therapy, given at a dose of 4 Gy.
These were hard-to-treat patients who had received multiple prior therapies since diagnosis, including carfilzomib, ibrutinib, bortezomib, anthracycline, and rituximab. In total, 8 of the patients had previously undergone autologous stem cell transplant and 11 were refractory to ibrutinib by the time of initial radiation therapy.
Median age of the patients was 69 years; 15 patients had classical histology and 4 had blastoid variant. Among the 98 tumor sites treated, the median tumor size was 2.8 cm.
In all, 14 patients received initial LDRT that was concurrent with chemotherapy. The remaining 5 patients had stopped chemotherapy prior to starting LDRT.
LDRT was given in 1-2 daily fractions via 3-dimensional conformal radiation therapy or electron beam.
Of the 98 tumor sites treated, complete response was achieved for 79 sites (81%) and the median time to complete response was 2.7 months after the start of LDRT. The researchers removed one patient who was an outlier with 27 tumor sites treated, and that dropped the complete response rate down to 76%. The overall response rate, which include an additional five sites with partial response, was 86%.
The researchers found links between complete response and soft tissue site versus non–soft tissue site (hazard ratio, 1.80; 1.12-2.90, P = .02). However, there were no associations between response and chemo-refractory status, ibrutinib-refractory status, prior chemotherapy courts, receipt of concurrent chemotherapy, tumor size, number of fractions, lesions treated per course, or blastoid variant.
The overall survival at 1 year after LDRT initiation was 90% and the 1-year progression-free survival was 55%. All five patients who died were refractory to ibrutinib.
The researchers reported finding no radiation therapy–related toxicities, even when patients received concurrent chemotherapy.
The use of LDRT has the potential to bridge refractory patients to subsequent therapies or to provide treatment breaks as patients recover from toxicities, the researchers said. However, they called for additional studies to confirm that this approach improves progression-free survival over chemotherapy alone.
The study was supported in part by a grant from the National Cancer Institute. The researchers reported having no competing financial interests.
SOURCE: Ning MS et al. Blood Adv. 2019. Jul 9;3(13):2035-9.