Within ranges of BCa stiffnesses, GelMA, GelSH and PEG-based hydrogels of 1–6 kPa stiffnesses successfully supported the growth and organoid formation of HR+,−/HER2+,− primary cancer cells at least to 2–3 weeks, with superior organoid formation within the GelSH biomaterial. The gene discussed is ERBB2; the disease is cancer.