Outcomes of patients treated with RCHOP with a PET adapted approach for consolidative radiotherapy: a retrospective single centre study at the Royal Marsden hospital

Treatment with CHOP based chemotherapy with consolidative radiotherapy (CRT) for primary mediastinal B cell lymphoma (PMBCL) has been the standard approach in the pre rituximab era. Overtreatment with CRT for patients who may have already been cured by primary immunochemotherapy in the Rituximab era is a significant concern due to the long term toxicity associated with radiotherapy. Positron emission tomography (PET) may help to identify patients who may not benefit from further CRT. We conducted a retrospective review of patients treated at the Royal Marsden hospital between 2003-2020 for PMBCL to assess CRT use and survival outcomes. 43 patients were identified, with 95% of the patients receiving R-CHOP. CRT was given in 5 patients. 5 year event free survival was 79% (95% confidence interval: 64% to 89%) and 5 year overall survival was 88% (95% confidence interval: 73% to 95%). 7/9 patients with DS4 did not receive CRT and instead monitored with serial PET scans. None of these 7 patients relapsed in the mediastinum. CRT may be omitted in patients with a negative EOT PET scans however careful observation may also obviate the need for CRT in PET positive patients. Micro abstract Chemotherapy followed by consolidative mediastinal radiotherapy has been the standard treatment for primary mediastinal B cell lymphoma however there are long term side effects associated with radiotherapy. We retrospectively reviewed outcomes of patients treated at our institution using a PET guided approach that identified patients suitable for surveillance rather than radiotherapy following chemotherapy.