MMP13 in PyMT Tumor Fibroblast Figure 4. MMTV-PyMT primary tumor growth and metastasis is not influenced by MMP13. (A) MMTV-PyMT tumor growth determined by weekly caliber measurements. Total tumor volumes are presented as mean +/2 the SEM. (N) MMTV-PyMT;Mmp13+/+, n = 38, (m) MMTV-PyMT;Mmp132/2, n = 25 . Three MMTV-PyMT;Mmp13+/+ mice were terminated before the end of the experiment due to extensive tumor burden, one at 8 weeks and two after 12 weeks. (B) MMTV-PyMT tumor growth determined by weekly caliber measurements in another cohort. (N) MMTV- PyMT;Mmp13+/+, n = 6, (m) MMTV-PyMT;Mmp132/2, n = 7. The total weight of the tumors at 11 weeks was 1.42g60.22 SEM for the MMTV- PyMT;Mmp13+/+ mice and 1.44g60.16 SEM for the MMTV-PyMT;Mmp132/2 mice. (C) Nuclear grading of the MMTV-PyMT tumors. Nuclear grading was performed on representative H&E stained sections from mammary tumors glands #1–3 from 13-week-old MMTV-PyMT;Mmp13+/+ (n = 34) and MMTV-PyMT;Mmp132/2 (n = 24) mice by a pathologist (FR) unaware of the genotypes. Nuclear grading was independent of genotype. (D) Lung metastasis volumes determined by stereology using Cavalieri’s principle. The total metastasis volume was determined in lungs obtained from the 13-week-old mice by an observer unaware of the genotypes. Median values are 1.2 mm3 in the MMTV- PyMT;Mmp13+/+ (n = 35) and 0.7 mm3 (n = 25) in MMTV-PyMT;Mmp132/2 mice, respectively. doi:10.1371/journal.pone.0002959.g004 Since MMP13 is upregulated concomitantly with the onset of cancer cell dissemination in the MMTV-PyMT model [16], we determined the metastatic burden in the lungs from end-stage MMTV-PyMT;Mmp13+/+ and MMTV-PyMT;Mmp132/2 mice using a morphometric approach [29]. Although there was a trend for a reduced lung metastatic volume in the absence of MMP13, this was not significant (Fig. 4D, 1.2 mm3 for MMTV-PyMT;Mmp13+/+, n = 35; 0.7 mm3 for MMTV-PyMT;Mmp132/2, n = 25, p = 0.34). We therefore conclude that the absence of MMP13 does not affect lung metastasis in the MMTV-PyMT breast cancer model. PLoS ONE | www.plosone.org 6 August 2008 | Volume 3 | Issue 8 | e2959