Clinical Scorecard: Characteristics and Treatment Obstacles in HER2-Positive Primary Breast Squamous Cell Carcinoma: A Case Study and Review of Existing Literature

At a Glance

Key Highlights

• HER2-positive PBSCC is extremely rare, with fewer than 100 cases reported globally.
• Standard HER2-targeted therapies show low efficacy in PBSCC, with a pathological complete response rate of only 12.5%.
• Acquired resistance mechanisms include HER2 antigen loss and PIK3CA mutations.
• Molecularly-guided precision therapy is recommended after failure of HER2-targeted treatments.
• Trastuzumab deruxtecan (T-DXd) has limited efficacy in HER2-positive PBSCC.

Guideline-Based Recommendations

Diagnosis

• Confirm HER2 positivity through immunohistochemistry and fluorescence in situ hybridization.

Management

• Consider neoadjuvant therapy with TCHP regimen, but be aware of potential inadequate responses.

Monitoring & Follow-up

• Regular imaging and molecular profiling to assess treatment response and resistance mechanisms.

Risks

• High risk of local recurrence and metastasis despite treatment.

Patient & Prescribing Data

Patients diagnosed with HER2-positive PBSCC.

Second-line therapy with pyrotinib plus capecitabine may provide disease control; however, response duration is variable.

Clinical Best Practices

• Utilize molecular profiling to guide therapy after initial HER2-targeted treatment failure.
• Prioritize agents targeting specific molecular alterations over continued HER2-targeted therapies.

Related Resources & Content

• Existing Literature on HER2-positive PBSCC