Clinicopathologic Characteristics of MYC Copy Number Amplification in Breast Cancer

Introduction: MYC overexpression is a known phenomenon in breast cancer. This study investigates the correlation of MYC gene copy number amplification and MYC protein overexpression with coexisting genetic abnormalities and associated clinicopathologic features in breast cancer patients. Methods: The study analyzed data from 81 patients with localized or metastatic breast cancers using targeted next-generation sequencing and MYC immunohistochemical studies, along with pathological and clinical data. Results: Applying the criteria of MYC/chromosome 8 ratio ≥5, MYC copy number amplified tumors (n = 11, 14%) were associated with invasive ductal carcinoma (91% vs 68%, P =.048), poorly differentiated (grade 3, 64% vs 30%, P =.032), mitotically active (Nottingham mitotic score 3, 71% vs 20%, P =.004), estrogen receptor (ER)-negative (45% vs 12%, P =.008), and triple-negative (56% vs 12%, P =.013) compared to MYC non-amplified tumors. Among MYC-amplified breast cancer patients, those with triple-negative status showed significantly shorter disease-free survival time than non-triple negative MYC-amplified patients (median survival month: 25.5 vs 127.6, P =.049). MYC amplification is significantly associated with TP53 mutation (P =.007). The majority (10 of 11; 91%) of MYC-amplified tumors showed positive c-MYC immunostaining. Conclusion: Breast cancers with MYC copy number amplication display distinct clinicopathologic characteristics indicative of more aggressive behavior.