Historical Perspective of HER2 Testing and Treatment in Prostate Cancer

Area of Science:

• Oncology
• Molecular Biology
• Pathology

Background:

• Human Epidermal Growth Factor Receptor 2 (HER2) is linked to poor prognosis in prostate cancer.
• Previous HER2-targeted therapies showed limited efficacy, but antibody-drug conjugates (ADCs) like trastuzumab deruxtecan (T-DXd) show promise.
• Accurate HER2 expression assessment is crucial for effective T-DXd treatment in prostate cancer.

Purpose of the Study:

• To develop and validate a modified HER2 immunohistochemistry (IHC) scoring system tailored for prostate cancer.
• To evaluate the clinical response of metastatic prostate cancer patients treated with T-DXd based on the new scoring system.
• To review historical HER2 testing in prostate cancer and identify factors limiting prior trial success.

Main Methods:

• Development of a novel HER2 IHC scoring system considering unique prostate tumor expression patterns.
• Classification of two metastatic prostate cancer patients as HER2 IHC 3+ using the new system.
• Review of past HER2 testing methodologies and clinical trial outcomes in prostate cancer.

Main Results:

• Two patients with metastatic prostate cancer classified as HER2 IHC 3+ by the new system showed significant clinical responses to T-DXd.
• The modified scoring system accounts for distinct HER2 spatiotemporal expression in prostate tumors.
• Historical analysis suggests previous HER2 trials may have failed due to inadequate scoring systems.

Conclusions:

• A standardized, prostate cancer-specific HER2 IHC scoring model is needed.
• This model can improve the predictive value of HER2 expression for T-DXd therapy.
• Accurate HER2 assessment is key to identifying prostate cancer patients who will benefit from HER2-targeted ADCs.