Durable Remissions Achieved with R-CHOP Chemotherapy without Radiotherapy in Patients with Primary Mediastinal B-Cell Lymphoma - the Royal Marsden Experience

Abstract Introduction: Primary mediastinal B Cell Lymphoma (PMBL) is a high-grade non-hodgkin lymphoma with distinct clinical and biological features. Optimal chemotherapy for this lymphoma is not established but some centres favour more intensive regimes such as DA EPOCH-R over R-CHOP. The role of consolidation radiotherapy is yet to be clarified and whether it can be omitted in those patients with a negative end-of-treatment PET scan (EOT PET) regardless of induction chemotherapy. Furthermore, the occurrence of false positive EOT PET scans may lead to overtreatment. The aim of this study was to establish the outcomes of patients (pts) with PMBL who had been treated in a single centre. Methods: Pts diagnosed with PMBL between 2003 and 2015 in Royal Marsden Hospital were included. Data was collected from electronic patient records and PET CT images review. Survival was defined from date of diagnosis until date of death or date of last follow up. Results: Thirty-four pts were identified with characteristics as shown in the table. Median diameter of the mediastinal mass was 12cm (range 5.5 - 24cm); 25 (74%) pts had a mass of ≥ 10cm. The majority of pts received R-CHOP chemotherapy (2 had 14 day cycles, 30 had 21 day cycles), 1 R-GCVP and another R-PACEBOM. Median number of cycles of chemotherapy was 6 (range 1-8). Seven out of 32 (22%) pts received involved field radiotherapy (IFRT). EOT PET was available for 30 pts. Median time to obtaining EOT PET from completion of chemotherapy was 31 days (20-81). Twenty-three out of 30 pts had EOT PET negative disease with a Deauville score (DS) of 1-3. Twenty-one of these 23 pts did not receive IFRT. Two of these 21 pts relapsed in the mediastinum and were treated with salvage chemotherapy followed by autologous stem cell transplant (ASCT) of whom 1 died due to their lymphoma. The 2 patients who received consolidation radiotherapy remain in remission. Seven out of 30 pts had a positive EOT PET (DS 4-5); of whom 5 received IFRT. Two out of 5 patients relapsed and proceeded with further chemotherapy of whom 1 died due to treatment-related causes while the other 4 patients were alive at time of last follow-up. Two pts with a positive EOT PET did not have IFRT, 1 proceeded with salvage chemotherapy but died due to lymphoma and the other patient was followed up with serial PET scans and ultimately the residual avidity was considered to be due to thymic hyperplasia. Conclusion: Our analysis demonstrates that for the 23 patients who achieved a complete metabolic response on EOT PET the risk of relapse was low (9%) (despite that only 2 patients received consolidation radiotherapy) and only one patient (4%) died of lymphoma. Thus the majority of patients with a negative EOT PET scan following R-CHOP chemotherapy may not need consolidation radiotherapy. This finding should be taken into account when considering the risk/benefit of adding radiotherapy treatment to patients who are already in metabolic CR after chemotherapy. Consolidation radiotherapy is currently being investigated in a prospective IELSG37 trial, NCT01599559. Table. Table. Disclosures Chau: Eli-Lilly: Honoraria, Other: Advisory Board, Research Funding; Bristol Meyers Squibb: Other: Advisory Board; MSD: Other: Advisory Board; Bayer: Other: Advisory Board; Roche: Other: Advisory Board; Merck Serono: Other: Advisory Board, Research Funding; Five Prime Therapeutics: Other: Advisory Board; Astra-Zeneca: Other: Advisory Board; Janssen-Cilag: Research Funding; Sanofi Oncology: Research Funding. Cunningham:Roche pharmaceuticals: Research Funding.