This case report, published in the Annals of Internal Medicine, details the remarkable response of a 60-year-old Air Force veteran with stage four metastatic prostate cancer to treatment with trastuzumab deruxtecan (T-DXd). The patient, who had not responded to multiple lines of therapy, was treated with T-DXd as a last resort after testing positive for HER2. T-DXd, an antibody drug conjugate, is FDA-approved for various HER2-expressing solid tumors, but its use in prostate cancer is novel. This marks the first known case of utilizing T-DXd for this type of cancer.
The case is particularly interesting because, after just four cycles of T-DXd, the patient experienced a 57% reduction in tumor volume, including in the brain. His condition significantly improved, defying previous prognoses that suggested hospice care due to limited treatment options. Nine months into the treatment, the patient remains clinically well, contrasting with the three to four months of effectiveness observed with previous treatments. This positive outcome highlights the potential of T-DXd for treating aggressive prostate cancer and emphasizes the importance of routine HER2 expression testing in advanced cases. This could lead to the identification of more patients who might benefit from targeted therapies like T-DXd.

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