Loss of Postn does not affect tumor growth in MMTV-Neu mice. (A and B) Representative mammary gland whole mounts from 4 month old virgin females showing multiple tumor foci in both wildtype and Postn(-/-) mice. (C-F) H & E staining of representative tumors collected at end point from wildtype (C and E) and Postn-null (D and F) mice. Both cystic (C and D) and solid tumors (E and F) were observed. (G) Kaplan-Meier survival analysis of tumor-bearing mice. Log rank testing showed no significant delay in tumor progression for Postn(-/-) mice when compared to heterozygotes or wildtype mice. All three genotypes reached end point with similar kinetics. (H-K) Paraffin-embedded sections were stained for ErbB2 (H and J) or Postn (I and K). Tumors arising in Postn-null females retained Neu expression. In Neu-induced tumors, Postn expression was restricted to the stromal compartment and was never found in the tumor cells. (L) Western blot analysis of mammary tumors (T) and whole gland (G) lysates. Supporting the IHC data, Postn was found to be expressed at low levels in tumors containing a small amount of stromal fibroblasts.