Effect of THPO-ASO treatment on breast cancer propagation in MMTV-PyMT mice. (A) Response to THPO-ASO was determined in a feasibility study by measuring the platelets count in untreated, saline-treated, or THPO-ASO–treated FVB/N-Tg 634Mul/J transgenic (MMTV-PyVT) mice. Weekly treatment with saline (controls, n = 6, red line) or THPO-ASO (n = 6, blue line) was initiated at 40 days of age, and platelet counts were determined at 40, 60, and 80 days after birth. (B) The time of palpable mammary tumor diagnosis during saline (n = 15, red line) and during THPO-ASO treatment (n = 15, blue line). (C) The number of mammary glands with palpable tumor at 80 days of age in saline (n = 10) and THPO-ASO (n = 10) treatment groups. (D) Individual tumor volumes at 80 days of age in saline- (n = 36) and THPO-ASO–treated (n = 33) animals. (E) Growth curves showing the means of total tumor volumes during saline (n = 10, red line) or THPO-ASO (n = 10, blue line) treatment. The combined tumor volume of 2 cm³ was set as the humane endpoint. Any animal reaching this endpoint, shown as a dotted line on the graph, was euthanized in accordance with institutional policies. (F) Age of mice at the time of euthanasia (combined tumor volume of 2 cm³) in saline-treated (n = 10, red line) or THPO-ASO–treated (n = 10, blue line) mice. (G) Representative hematoxylin and eosin–stained lung sections obtained after euthanasia of mice. Scale bars, 1 mm. (H) The number of metastatic nodules in the lung at time of euthanasia in saline-treated (n = 6) or THPO-ASO–treated (n = 6) mice. The 2-tailed, unpaired Student t test was used for comparison of means in panels A and C-D. *P < .05; **P < .01; ***P < .001. Log-rank test was used for comparisons in panels B and F. ***P < .001.