(A) DNA PCR genotyping of Ddr2 alleles from whole tumors from indicated mice. (B) Western blot of CAFs isolated from MMTV-PyMT (WT) or FSP1cre; Ddr2fl/fl; MMTV-PyMT (Ddr2-/- FSP1cre) mice with the indicated antibodies. (C) Number of total lung metastases in MMTV-PyMT (WT) (n = 18 mice) or FSP1cre; Ddr2fl/fl; MMTV-PyMT (Ddr2-/-; FSP1cre) (n = 10 mice) mice at termination (@20 weeks or when a single tumor reached 2 cm). **p=0.0095. All mice were >99% FVB/n. Lung tumors were enumerated histologically. (D) Primary tumor growth rate in MMTV-PyMT (WT) (n = 18 mice) or FSP1cre; Ddr2fl/fl; MMTV-PyMT (Ddr2-/- FSP1cre) (n = 10 mice) as represented by time in weeks to end stage (single tumor 2 cm in largest dimension). (E) Total primary tumor burden in WT; MMTV-PyMT (WT) (n = 18 mice) or FSP1cre; Ddr2fl/fl; MMTV-PyMT (Ddr2-/- FSP1cre) (n = 10 mice). Represented as the total volume of all primary tumors per mouse. (F) FACS quantification of percent PDGFRα positive cells (i.e., CAFs) per total primary tumor in size- and age-matched MMTV-PyMT (WT) or FSP1cre; Ddr2fl/fl; MMTV-PyMT (Ddr2-/- FSP1cre) tumors. Four tumors each from four different mice were analyzed (total of 16 tumors). (G) Representative second harmonic images (SHG) of 10–12 week MMTV-PyMT (WT) or FSP1cre; Ddr2fl/fl; MMTV-PyMT (Ddr2-/- FSP1cre) tumors. Scale bars = 100 um. (H) Quantification of TACS1 and TACS2/3 phenotype in tumor analyzed in (H). Six tumors from three different mice per genotype were analyzed (total of 18 tumors). *p<0.05. (I) 2D en face rendering of 3D reconstructed FIB-SEM images of tumor-stromal boundary (2–5 μM) from 12 week old MMTV-PyMT (WT), ubiquitous Ddr2-/- null; MMTV-PyMT, or Ddr2-/-; FSP1cre; MMTV-PyMT tumors. Collagen fibers are green. Three tumors of each genotype were analyzed (n = 3 for each). See also Videos 1, 2 and 3. (J) Quantification of fiber width in pixels relative to WT from FIB-SEM images in (I) for indicated tumors (n = 3 for each genotype). Fibers were quantified with CT-FIRE software (LOCI, Madison, WI). ****p<0.0001, **p=0.0041. In all panels, statistics were one-way ANOVA with Tukey’s post hoc test. Unless otherwise noted, *p<0.05, **p<0.01, ***p<0.001, ns no significant difference.