Background Procarbazine-containing chemotherapy regimens associate with cytopenias and infertility, suggesting stem cell toxicity. Procarbazine in eBEACOPP (escalated dose bleomycin, etoposide, doxorubicin, cyclophosphamide, vincristine, procarbazine, prednisolone) is increasingly replaced with dacarbazine (eBEACOPDac) to reduce toxicity, although limited genomic and clinical data support this substitution. Methods To assess mutagenic and clinical consequences of dacarbazine-procarbazine substitutions, we compared mutational landscapes in haematopoietic stem and progenitor cells (HSPCs) from patients treated with different Hodgkin regimens and children, sperm and bowel tissue from procarbazine-treated patients. We compared efficacy and toxicity data of a multicentre eBEACOPDac-treated patient cohort, with eBEACOPP clinical trial and real-world datasets. Results eBEACOPP-treated patients exhibit a higher burden of point mutations, small insertions and deletions in HSPCs compared to eBEACOPDac and ABVD (doxorubicin, bleomycin, vinblastine, dacarbazine)-treated patients. Two novel mutational signatures, SBSA (SBS25-like) and SBSB were identified in HSPCs, neoplastic and normal colon from only procarbazine-treated patients. SBSB was also identified in germline DNA of three children conceived post-eBEACOPP and sperm of an eBEACOPP-treated male. The dacarbazine substitution did not appear to compromise efficacy; 3-year progression-free survival of 312 eBEACOPDac patients (93.3%; CI95=90.3-96.4%) mirrored that of 1945 HD18-trial eBEACOPP patients (93.3%; CI95=92.1-94.4%). eBEACOPDac-treated patients required fewer blood transfusions, demonstrated higher post-chemotherapy sperm concentrations, and experienced earlier resumption of menstrual periods. Conclusions Procarbazine induces a higher mutational burden and novel mutational signatures in eBEACOPP-treated patients and their germline DNA raising concerns for hereditary consequences. However, replacing procarbazine with dacarbazine appears to mitigate gonadal and stem cell toxicity while maintaining comparable clinical efficacy.

The authors have declared no competing interest.

The study was funded by the Addenbrooke's Charitable Trust. The study was funded by the Wellcome Trust.

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The Health Research Authority of England and Wales gave ethical approval for this work. The Public Benefit and Privacy Panel of Scotland gave ethical approval for this work. The NHS Research Ethics Committee gave ethical approval for this work (REC reference 18/EE/0199, IRAS 149581).

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