Abstract
Despite the importance attributed to exercise training in the breast cancer (BC) continuum,
the underlying mechanisms modulating tumor behavior are unknown. We evaluated the
effects of long-term moderate-exercise in the development of mammary tumors, and studied
the microenvironment of infiltrative lesions, the amount of connective tissue, and
balance between cellular proliferation/death.
Fifty Sprague-Dawley rats, randomly assigned into four groups: two control groups
(sedentary and exercised) and two models of BC groups (sedentary and exercised) induced
by N-methyl-N-nitrosoureia (MNU), were sacrificed after 35 weeks of moderate-exercise,
and all perceptible tumors were removed for histological and immunohistochemistry
analysis.
The median number of infiltrative-lesions per animal was lower in the MNU exercised
animals (p=0.02). More than one histological pattern was identified, and papillary
carcinoma was the most frequent in both groups. Within infiltrative-lesions, the number
of immunopositive cells per μm2 of Ki67 was lower in exercised animals (p=0.002). This presents increased cell death
per μm2 (p=0.019). Tumors from sedentary animals had a higher expression of collagen deposition
(p=0.027).
Long-term moderate-exercise has beneficial effects in tumor development with a diminished
prevalence of malignancy. Within infiltrative-lesions, moderate-exercise improves
the balance between cell-proliferation and cell-death with decreased connective tissue
that suggests lower tumor aggressiveness.
Key words
breast tumor - exercise training - ki67 - cell death - TUNEL assay - cell proliferation
- collagen content
