Hormone-Induced Protection of Mammary Tumorigenesisin Genetically Engineered Mouse Models - Genetic Engineering: Recent Developments in Applications - page 279

Figure 9. Effect of short-term hormone treatment on tumor growth rate in the activated Her-2/neu transgenic
mice. Treatment with estradiol alone or estradiol plus progesterone significantly increased the time taken for the
mammary tumors to grow from initial palpation to a diameter of 1 cm in comparison with the controls. Results
are expressed as means ± SEM.
Mice were examined twice weekly beginning after the hormone treatments,
and the earliest tumors were detectable by palpation (Figure 9). The sizes of tu-
mors were recorded after each examination. In control mice the average age at
which palpable tumors were first detected was 95 days. Tumors were initially
palpated 142 days in estradiol-treated mice and at 138 days in mice treated with
estradiol plus progesterone. Tumor growth was monitored until the tumor in each
mouse had reached a diameter of 1 cm. The difference in tumor growth rate be-
tween the control and hormone-treated mice was significant. There was almost a
threefold difference in the time required for the mammary tumors to grow to 1
cm in diameter (after initial palpation) in mice treated with estradiol or estradiol
plus progesterone compared with the controls.
Real-time PCR analyses demonstrated that expression of the transgene was not
significantly altered by the transgene in the normal mammary tissue, mammary
tumors and the mammary tissue adjacent to the mammary tumor. There was a
significant difference in the expression levels of cyclin D1 (Figure 10). Mammary
tumors from the control group had a significantly higher (about 5.6-fold) expres-
sion of cyclin D1 in comparison with animals treated with estradiol alone or
estradiol plus progesterone.