Correlative science (CS) can potentially augment clinical trial results by identifying biomarkers of response and resistance to a novel intervention. We evaluated recently published breast cancer phase II trials (BP2T) to determine prevalence, characteristics, and outcomes of CS. Through Pubmed, we identified BP2T of systemic therapy published between June 2005 and June 2010. A study-specific abstraction tool recorded trial characteristics, CS endpoints, source of tissue, adequacy of samples, biopsy safety, and CS outcomes. BP2T authors were contacted to verify abstraction results. Results were abstracted from 298 eligible trials enrolling 18,782 patients, of which 81 (27.2 %) involved CS. Of these, 57 (70.4 %) included tissue with 16 (28 %) using optional research biopsies and 17 (30 %) requiring mandatory research biopsies. No trial addressed biopsy safety issues. Trials were more likely to include CS if they were: industry versus non-industry sponsored (33.7 % vs. 17.1 %, p = 0.0017), neoadjuvant versus metastatic setting (47 % vs. 21.2 %, p = 0.0001), or U.S. versus non-U.S. trials (37 % vs. 21 %, p = 0.005). A minority of phase II breast cancer trials include CS representing a missed opportunity to learn more from clinical research. When CS is included, consistent reporting of endpoints, feasibility, outcomes, and safety is needed.