Breast cancer research is highlighting targetable biology in endocrine-resistant disease. A British Journal of Cancer report dated April 4, 2026 identifies molecular profiles that define antiprogestin-resistant breast cancer, pointing to markers that could be used to stratify resistant tumors and guide therapy selection. In small cell lung cancer, a separate research update describes how molecular profiles can help guide targeted and immunotherapy selection in a disease defined by extensive heterogeneity. The focus is on mapping variations that may explain differential treatment sensitivity. Both findings add to a broader precision-oncology toolkit—moving from histology to biomarker-defined subgroups where resistance and response can be mapped more directly.