Researchers from the George Washington University and the Washington DC Veterans Affairs Medical Center have published a case report that signifies a potential breakthrough in the treatment of an aggressive type of prostate cancer.

The report centers around a 60-year-old Air Force Veteran diagnosed with stage four metastatic prostate cancer and the positive outcomes of being treated with trastuzumab deruxtecan (T-DXd), an antibody drug conjugate.

The patient did not respond to multiple lines of therapy and experienced persistent tumor progression. As a last resort, the researchers tested for HER2 by immunohistochemistry, which came back positive and the patient was treated off-label in February 2024 with T-DXd.

The antibody drug conjugate, which is FDA approved for the treatment of a variety of HER2-expressing solid tumors including breast cancer, has not been studied in prostate cancer.

Maneesh Jain, senior researcher and oncologist at the GW School of Medicine and Health Sciences and attending physician in the Section of Hematology & Medical Oncology at the Washington DC VA Medical Center treated this patient, which is the first known case of using T-DXd for prostate cancer treatment.

The case report, "Response of Human Epidermal Growth Factor Receptor 2–Expressing Prostate Cancer to Trastuzumab Deruxtecan" was published November 5, 2024 in the Annals of Internal Medicine.

After four cycles of T-DXd, the patient showed a 57% overall reduction in tumor volume, including in the brain. His condition improved significantly, defying earlier prognoses that suggested a transition to hospice care due to a lack of treatment options. As of November 2024, the patient is clinically doing well. He has been on this therapy now for nine months, while the last three lines of treatment for his advanced prostate cancer worked only three to four months each.

"This case highlights the promising potential of T-DXd in treating prostate cancer patients, particularly in aggressive forms," said Jain. "It also underscores the importance of routine HER2 expression testing in advanced prostate cancer, which could help identify more patients who might benefit from targeted therapies like T-DXd."