Tumorigenicity of 3 types of R2N1d cells in immune-deficient mice. Adherent (CD44+/CD24- sorted), non-adherent and re-attached R2N1d cells were inoculated subcutaneously into nude mice for tumor development. Only those mice inoculated with adherent and reattached R2N1d cells showed visible and palpable tumors 4 weeks after inoculation; Mice inoculated with non-adherent R2N1d cells developed tumors after 24 weeks. Histological sections of resected tumor harvested at 4 weeks (from adherent and reattached cells) or 24 weeks (from non-adherent cells) showed HER2 expression. The length of the scale bar of these photos is 100 μm.