Clinical relevance of receptor conversion in metastatic breast cancer: Case report

INTRODUCTION: Breast cancer comprises several different pathological entities defined by the presence or absence of hormonal receptors and human epidermal growth factor receptor 2 (HER2). During the disease course, the increase in tumor heterogeneity contributes to the discordant expression of estrogen/progesterone receptors and HER2 status between primary and metastatic lesions. We describe a case that demonstrates the clinical relevance of molecular reassessment during metastatic breast cancer progression. PATIENT CONCERNS: A 40-year-old Caucasian woman with germline breast cancer gene mutation was referred to a general surgery appointment after breast ultrasound revealed a suspicious nodular lesion in 2012. DIAGNOSIS: Ultrasound-guided microbiopsy revealed an invasive ductal carcinoma of no special type, hormone receptor-positive, and HER2-negative. INTERVENTIONS: The patient underwent modified radical left mastectomy, adjuvant radiotherapy, chemotherapy, and endocrine therapy. Four years after the diagnosis, HER2 positive lung progression was documented, and the patient received anti-HER2 targeted systemic therapy for 15 months. New disease progression with a triple-negative profile was found, and palliative systemic treatment was changed to carboplatin for 3 months until new progression. Based on the results of the OlympiAD trial, monotherapy with Olaparib 300 mg twice daily for 28 days was initiated. OUTCOMES: After seven cycles of treatment, patient showed progressive improvement in quality of life and maintained stable disease without significant adverse events. CONCLUSION: The clinical relevance of hormone receptor and HER2 status discordance between primary tumors and metastatic lesions has been studied in recent years. This case report illustrates the clinical impact of molecular changes during disease progression and the adaptation of treatment options. This allows for an increase in both survival and quality of life in patients with metastatic breast cancer.