Background and importance Very significant therapeutic advances have been made with regard to immunotherapy in the treatment of metastatic melanoma. The use of monoclonal antibodies, particularly pembrolizumab, has shown encouraging results in terms of efficacy and survival in cancer patients, but some patients develop adverse reactions that can sometimes be fatal, or their management may require temporary or permanent interruption of treatment.

Aim and objectives We report the case of a patient who had immunological adverse reactions to pembrolizumab for metastatic melanoma.

Material and methods A 59-year-old patient was managed for lower limb melanoma in advanced locoregional evolutionary pursuit classified as T3b N3 M0. The absence of a BRAF mutation led to the introduction of immunotherapy with the anti-PD1 antigen pembrolizumab. Two weeks after the second injection, an initial and transient increase in tumour size with the appearance of new small lesions was noticed, associated with intense fatigue, taste alteration with loss of appetite and constipation. After the third injection, a false progression of the tumour was noticed, requiring discontinuation of treatment. The patient was hospitalised for undernutrition with sudden weight loss, asthenia and general deterioration. Biological examinations revealed anaemia with severe undernutrition. Fatigue and altered condition did not allow the patient to undergo scheduled chemotherapy. The patient died within 3 months. The accountability study was carried out in accordance with the French method.

Results In this case, pembrolizumab was implicated with an imputability score of I5 B4, according to the French method.

Conclusion and relevance New immunotherapy approaches are characterised by a range of new toxicities that must be known, not only by medical oncologists and by all those involved in the management of oncology patients. Early detection of immunological toxicities and early application of available algorithms allow for complete resolution of symptoms in the majority of cases. However, if these symptoms are neglected, the development can lead to serious toxicities, including death of the patient.

References and/or acknowledgements 1. Kennedy LB, Salama AKS. Oncol Ther 2019. https://doi.org/10.1007/s40487-019-0096-8

2. Levy D, Dhillon HM, Lomax A, et al. Certainty within uncertainty: a qualitative study of the experience of metastatic melanoma patients undergoing pembrolizumab immunotherapy. Supportive Care in Cancer 2018;1–8. 2/Cappelli L.

No conflict of interest.