The genomic and clinical consequences of replacing procarbazine with dacarbazine in escalated BEACOPP for Hodgkin lymphoma: a retrospective, observational study

Background Procarbazine-containing chemotherapy regimens are associated with cytopenias and infertility, suggesting stem-cell toxicity. When treating Hodgkin lymphoma, procarbazine in escalated-dose bleomycin- etoposide-doxorubicin-cyclophosphamide-vincristine-procarbazine-prednisolone (eBEACOPP) is increasingly replaced with dacarbazine (eBEACOPDac) to reduce toxicity. We aimed to investigate the impact of this drug substitution on the mutation burden in stem cells, patient survival, and toxicity. Methods In this two-part retrospective, observational study, we first compared mutational landscapes in haematopoietic stem and progenitor cells (HSPCs) from patients with advanced-stage Hodgkin lymphoma in remission for at least 6 months who had been treated with eBEACOPDac (eBEACOPDac cohort), eBEACOPP (real- world eBEACOPP cohort), or doxorubicin-bleomycin-vinblastine-dacarbazine (ABVD); in buccal DNA from five children of a female patient with classical Hodgkin lymphoma treated with eBEACOPP before conceiving the third child; in sperm DNA from a patient with mild oligospermia treated with eBEACOPP; and in caecal adenocarcinoma and healthy colon tissue from a survivor of Hodgkin lymphoma treated with chlorambucil- vinblastine-procarbazine-prednisolone. For the second part, we analysed efficacy and toxicity data from adult patients (aged >16 years) treated with first-line eBEACOPDac (eBEACOPDac cohort) at 25 centres across UK, Ireland, and France; efficacy was compared with the German HD18 eBEACOPP trial data and toxicity with a UK real- world dataset. Participants in the German HD18 and UK real-world datasets were adults (aged >16 years) with previously untreated Hodgkin lymphoma, treated with first-line eBEACOPP. We had two co-primary objectives: to define the comparative stem-cell mutation burden and mutational signatures after treatment with or without procarbazine-containing chemotherapy (first study part); and to determine progression-free survival of patients with Hodgkin lymphoma treated with eBEACOPP or eBEACOPDac (second study part). Secondary objectives included overall survival and explored differences in specific toxicity outcomes, including transfusion requirements and measures of reproductive health (second study part). Findings In the first part of the study (mutational analysis), patients treated with eBEACOPP (n=5) exhibited a higher burden of point mutations in HSPCs compared with those treated with eBEACOPDac (n=4) or ABVD (n=3; excess mutations 1150 [95% CI 934-1366] vs 290 [241-339] vs 186 [116-254]). Two novel mutational signatures, SBSA (SBS25-like) and SBSB, were identified in HSPCs and in a single neoplastic and healthy colon sample from patients who received procarbazine-containing chemotherapy. SBSB was also identified in germline DNA of three children conceived after eBEACOPP and in sperm of a male patient treated with eBEACOPP. SBSC was detected in patients treated with either ABVD or eBEACOPDac. In the second part of the study (efficacy and toxicity analysis), dacarbazine substitution did not appear to compromise efficacy or safety. 312 patients treated with eBEACOPDac (eBEACOPDac cohort; treated 2017-22, 186 [60%] male, median follow-up 36<middle dot>0 months [IQR 25<middle dot>2-50<middle dot>1]) had a 3-year progression-free survival of 93<middle dot>3% (95% CI 90<middle dot>3-96<middle dot>4), which was similar to the 93<middle dot>3% [95% CI 92<middle dot>1-94<middle dot>4]) progression-free survival seen in 1945 patients in the German HD18 eBEACOPP trial (treated 2008-14, 1183 [61%] male, median follow-up 57<middle dot>0 months [35<middle dot>4-64<middle dot>7]). Patients treated with eBEACOPDac required fewer blood transfusions (mean 1<middle dot>70 units [SD 2<middle dot>77] vs 3<middle dot>69 units [3<middle dot>89]; p<0<middle dot>0001), demonstrated higher post-chemotherapy sperm concentrations (median 23<middle dot>4 million per mL [IQR 11<middle dot>0-632<middle dot>3] vs 0<middle dot>0 million per mL [0<middle dot>0-0<middle dot>001]; p=0<middle dot>0040), and had earlier resumption of menstrual periods (mean 5<middle dot>04 months [SD 3<middle dot>07] vs 8<middle dot>77 months [5<middle dot>57]; p=0<middle dot>0036) compared with 73 patients treated with eBEACOPP in the UK real-world dataset. Interpretation Procarbazine induces a higher mutation burden and novel mutational signatures in patients with Hodgkin lymphoma treated with eBEACOPP and their germline DNA, raising concerns for the genomic health of survivors of Hodgkin lymphoma and hereditary consequences for their offspring. However, replacing procarbazine with dacarbazine appears to mitigate gonadal and stem-cell toxicity while maintaining similar clinical efficacy.