Furthermore, 5/7 mice implanted with Hpa2 cells exhibited metastatic lesions also in the opposite mammary gland (Supplementary Fig. 4A, black arrows; Supplementary Fig. 4B), implying that MDA-MB-231 cells over-expressing Hpa2 develop more aggressive and more metastatic disease. The gene discussed is HPSE2; the disease is metastatic neoplasm.