SS18–SSX and Smarcb1 compete in the balance between sarcomagenesis and tumor suppression, driving different phenotypes. A, Schematic for TATCre protein injection into the paw and gross images of a tumor that developed over a year later in a Smarcb1fl/fl mouse. B, Schematic of the expression and recombination pattern from Myf5Cre and a mouse with anatomic distribution of Myf5Cre; Smarcb1fl/fl and Myf5Cre;hSS2 tumors from 16 consecutive mice in each group (two-tailed Fisher exact test for incidence of tumors in each cohort, P = 0.0002; χ2 = 17.03 with four degrees of freedom and P = 0.0019 for comparing distributions of tumors in each cohort). C, Distribution of tumor size versus time at morbidity among cohorts of hSS2/wt and hSS2/hSS2 mice in which sarcomagenesis was initiated at age 4 weeks by hind-limb injection of TATCre (two-tailed t test, P = 6.6 × 10−5 for time to tumorigenesis). D, Kaplan–Meier (KM) plot of the tumor-free fraction among cohorts of hSS2-heterozygous mice bearing each possible Smarcb1-floxed genotype (in magenta) after TATCre injection into the hind limb at age 4 weeks. (The cohort of hSS2-het–alone is data from the cohort depicted in Fig. 2A for reference; the other two cohorts are littermate-controlled cohorts: Smarcb1fl/wt compared with Smarcb1fl/fl, log-rank test z = 4.43, P < 0.001.) E, Tumor growth by caliper measurements in littermate cohorts of mice homozygous for hSS2 and either wild-type or Smarcb1fl/fl genotype following TATCre injection at age 4 weeks (two-tailed t test, P = 1.3 × 10−8 for time to detectable tumor). F, KM plot of Myf5Cre-induced combination genotype tumors compared with either hSS2 or Smarcb1fl/fl alone (log-rank tests comparing combination genotype to Smarcb1fl/fl alone, z = 4.62, P < 0.0001; to hSS2 alone, z = 8.15, P < 0.0001). G, Representative hematoxylin and eosin photomicrographs of tumors from Smarcb1fl/fl, hSS2 heterozygous, combination hSS2 and Smarcb1fl/fl, and hSS2 homozygous mice activated by TATCre limb injection or Myf5Cre (scale bars = 20 μm). H, Graph of the fraction of tumors by each induction method demonstrating each of the histologic features (TATCre + Smarcb1fl/fl, n = 11; Myf5Cre;Smarcb1fl/fl, n = 8; TATCre + hSS2, n = 15; Myf5Cre;hSS2, n = 17; TATCre + hSS2;Smarcb1fl/fl, n = 13; Myf5Cre;hSS2;Smarcb1fl/fl, n = 8). Pleio., pleiomorphism.