Triterpenoids were identified as the main components of digested Chaga water extract, which was able to reduce cancer cell viability, to interfere with oncogenic signaling pathways and to induce a cell cycle G0/G1-phase arrest in both triple-negative (MDA-MB-231) and HER2-positive (SK-BR-3) BC cell lines. The gene discussed is ERBB2; the disease is breast cancer.