Human triple-negative breast cancer cell lines are invasively heterogeneous. (A) High magnification images (20× and 63×) of E-cadherin immunofluorescence on 3D spheroids of 4T1 leaders, followers, and singles. Green in the overlay image denotes nuclei fluorescence emitted from H2B-Dendra2 and red denotes E-cadherin staining. Scale bar, 50 µm. (B) Brightfield image of a SUM159 (10×) and HCC38 (20×) spheroid embedded in rat-tail collagen type I after 24 h invasion. Red circles denote collective chains and green circles denote single cells. Scale bar, 50 µm.