Melflufen, also known as melphalan flufenamide, is a peptide-drug conjugate designed to deliver an alkylating payload preferentially into myeloma cells by exploiting peptidase activity within the tumor microenvironment. The OCEAN trial compared melflufen-dexamethasone against pomalidomide-dexamethasone in patients with relapsed or refractory disease, while HORIZON evaluated melflufen in heavily pretreated patients. The current European approval restricts melflufen use to patients who have not undergone autologous stem cell transplant or whose time to progression is three years or more, a restriction grounded in a post-hoc analysis of OCEAN showing that patients with a time to progression under 36 months fared significantly worse on melflufen than on the comparator, with median overall survival of 15.7 versus 28.7 months and a hazard ratio of 1.8 that reached statistical significance.

The commentators focus their first major criticism on Patient 1 from the case series, whose time to progression after autologous stem cell transplant was 28 months, placing this individual squarely within the subgroup that the OCEAN post-hoc analysis identified as being disadvantaged by melflufen treatment. The original paper acknowledged this discrepancy only briefly, noting that the long duration of response occurred despite the unfavorable time to progression. Bhise and colleagues contend that this framing creates a subtle but consequential problem: a single case with an atypically favorable outcome is being used to soften the message about a subgroup that randomized trial evidence indicates is harmed, on average, by this treatment relative to the alternative. They emphasize that case reports are inherently susceptible to selective emphasis because exceptional outliers are precisely what prompt such reports in the first place.

The statistical logic underlying this criticism reflects a well-known pitfall in clinical evidence interpretation. Subgroup analyses of randomized trials estimate average effects within defined patient populations, and individual outcomes within any subgroup can deviate dramatically from that average without invalidating the population-level finding. When a case report highlights an outlier who thrived despite belonging to a subgroup that trial data show is disadvantaged, presenting that case alongside arguments for extending treatment to patients outside the approved population risks leaving readers with the impression that individual favorable responses can offset subgroup-level harm demonstrated in a randomized comparison. The commentators argue that explicitly restating, within the discussion of this specific case, that the OCEAN subgroup data indicate a significant survival disadvantage for similar patients would prevent the exceptional case from being misread as evidence against the very population-level finding it contradicts.

The second major criticism concerns the safety data used to reassure readers about the risk of second primary malignancies. Patient 1 received 46 cycles of melflufen-dexamethasone over approximately four years before developing a second primary myelodysplastic neoplasm, a type of bone marrow disorder that can progress to acute leukemia. The original authors attributed this malignancy largely to the patient’s prior exposure to alkylating agents and immunomodulatory drugs, citing the low reported rate of second primary malignancies across the HORIZON and OCEAN trials as reassurance about melflufen’s own mutagenic contribution. The commentators find this reassurance statistically unsound for a specific and important reason rooted in the relationship between cumulative exposure and carcinogenic risk.

That reason is exposure duration. The median progression-free survival among trial responders was 8.5 months in both study populations, meaning that most trial patients received only a small fraction of the cumulative melflufen exposure that Patient 1 accumulated before the malignancy developed. Cumulative-dose-related carcinogenesis is a well-established feature of alkylating agents, and the commentators point out that the trial population’s exposure was systematically too brief to detect such a risk even if it existed. A second primary malignancy rate calculated from a population whose treatment was, on average, cut short after several months by disease progression or intolerance therefore provides limited reassurance about mutagenic risk in patients who go on to receive several years of continuous alkylating exposure. Because the original discussion favors considering melflufen for extended use in exceptional responders, the very population capable of accumulating multi-year exposure, the safety reassurance drawn from short-exposure trial populations does not address the risk profile most relevant to the patients the recommendation would actually affect.

The commentators propose a concrete methodological remedy: reporting cumulative melflufen dose or treatment duration alongside second primary malignancy incidence, where such data are available from trial extensions or real-world follow-up, would provide a more directly applicable estimate of risk for long-term responders being considered for extended therapy. This recommendation aligns with broader principles in oncology pharmacovigilance, where the relevance of safety signals depends critically on matching the exposure profile of the safety data to the exposure profile of the patients in question. Similar concerns about second primary malignancies have been raised in other novel therapy contexts, including systematic reviews of malignancy risk following CAR T-cell therapy, underscoring that long-duration follow-up is essential whenever powerful cytotoxic or immunologic treatments achieve durable disease control.

Despite these pointed criticisms, the commentary is not a rejection of the original work. Bhise and colleagues explicitly acknowledge that the case series offers a genuinely useful clinical contribution by illustrating that meaningful, durable responses to melflufen-dexamethasone are achievable in carefully selected patients. They note that such granular, longitudinal case detail complements population-level trial reporting in ways that aggregate statistics cannot, capturing the clinical course of individual patients over years of treatment. They also credit the original authors with appropriate transparency for explicitly acknowledging that the cases were retrospectively selected for their exceptional duration of response, an admission that properly frames the study’s inherent selection bias. This balanced tone reflects a growing recognition in the medical literature that case reports retain value precisely when their limitations are stated plainly and their conclusions are calibrated to the strength of the evidence.

The clinical implication drawn by the commentators is direct and specific. Before these exceptional cases inform practical guidance about extending melflufen use beyond the currently approved target population or into multi-year continuous therapy, two reconciliations are needed. First, the discussion of Patient 1 should explicitly confront the unfavorable OCEAN subgroup data for patients with a time to progression under 36 months, rather than allowing a favorable outlier to stand in implicit tension with randomized evidence. Second, reassurance about second primary malignancy risk during extended use should be grounded in exposure-matched safety data rather than incidence rates drawn from a trial population whose average treatment duration was substantially shorter. Until those conditions are met, the commentators suggest, the exceptional responses should be viewed as intriguing observations rather than as a basis for broadening treatment recommendations.

The exchange highlights a broader lesson for the era of precision oncology and expanding immunotherapies. As treatment landscapes grow more complex, with novel agents such as antibody-drug conjugates, bispecific antibodies, and CAR T-cell therapies entering practice alongside older cytotoxic backbones, the temptation to generalize from spectacular individual responses will only increase. The commentary by Bhise, Akotkar, Bhandari, and Gite serves as a reminder that the evidentiary weight of a case report is bounded by the statistics of the trials that contextualize it, and that safety conclusions are only as strong as the exposure profiles on which they rest. For patients with relapsed or refractory multiple myeloma, a disease where treatment sequencing decisions carry profound survival consequences, the difference between an exceptional anecdote and population-level evidence can be a matter of years of life, making rigorous interpretation of both not an academic nicety but a clinical imperative.

Subject of Research: Critical appraisal of melflufen-dexamethasone case reports for relapsed/refractory multiple myeloma

Article Title: Comment on “Exceptional long-term responses from OCEAN and HORIZON trials: melflufen-dexamethasone as an expansion of treatment options for relapsed/refractory multiple myeloma in the era of new immunotherapies?”

Article References: Bhise, M. R., Akotkar, A., Bhandari, S., & Gite, K. V. (2026). Comment on “Exceptional long-term responses from OCEAN and HORIZON trials: melflufen-dexamethasone as an expansion of treatment options for relapsed/refractory multiple myeloma in the era of new immunotherapies?”. Journal of Cancer Research and Clinical Oncology, 152(9), Article 176. https://doi.org/10.1007/s00432-026-06608-4

Image Credits: AI Generated

DOI: 10.1007/s00432-026-06608-4

Keywords: melflufen, dexamethasone, multiple myeloma, OCEAN trial, HORIZON trial, relapsed/refractory myeloma, second primary malignancy, subgroup analysis, case report, alkylating agents, clinical trials, oncology