HECTD4 and neoplasm: Despite their high baseline tumorigenesis, MDA-MB-231 cells with shRNA-mediated HECTD4 knockdown (>80%) doubled in tumor size in immunosuppressed NSG mice, compared with sh-scramble controls (457.1 μg ± 118.1 vs. 204.9 μg ± 51.01, P = 0.0078; Fig. 2A and SI Appendix, Fig. S2A).