Latency and progression of mammary tumors in hypo and hyperthyroid rats.

LÓPEZ-FONTANA, C.; MASELLI, M.; GUIÑAZÚ, E.; JAHN, G.; CARÓN, R.

Mendoza

Congreso; 28° Reunión Científica Annual de la Sociedad de Biología de Cuyo; 2010

Sociedad de Biología de Cuyo

To determine whether mild hypo- and hyperthyroidism affect the incidence and progression of breast cancer (CaM), and in particular, apoptosis of tumor cells we design the present study. Female Sprague-Dawley rats were treated per os with a single dose of DMBA (15mg/rat) at 55 days of age and divided into three groups: euthyroid (EUT, n=10) with mild hyperthyroidism (HIPER, 0.25mg/kg/day, T4 sc, n=12) and mild hypothyroidism (HYPO, 0.01% PTU in drinking water, n=9). The latency, incidence and progression of tumors were determined in the three groups. When the tumors reached a volume >1000 mm3, the animals were decapitated and the tumors were removed and aliquotted for histopathological analysis and molecular studies. The apoptotic index was calculated by counting the apoptotic bodies in histological sections stained with hematoxylin and eosin with 60X objective. Statistical analysis was performed by ANOVA I and Bonferroni test or Kruskal-Wallis and Dunn, according to the normality of the variable. The incidence rates were analyzed by Chi square. The latency of onset of tumors was lower in HYPER (87.5+5.3 days) than HIPO (97.7+7.5 days) and EUT (91.1+4.8 days). The incidence tended to be higher in HYPER (75%) than in EUT (70%) and HIPO (33.3%). The tumor growth rate was higher in tumors HIPER and EUT than in HIPO (p <0.05). The histopathology was similar in the three groups, but the apoptotic index was significantly lower in HYPER compared to the other two groups (p = 0.02). Conclusions: The results so far suggest that apoptosis of breast tumors is diminished by hyperthyroidism, which could account for the trend in the latency, incidence and growth rate of the same. Molecular studies of apoptosis, currently underway, may confirm this relationship.