Estrogen receptor-alpha expression in spontaneous mammary tumors in Trp53+/- mice. Spontaneous mammary tumors from nulliparous (i-iii) and parous (iv-vi) BALB/c-Trp53+/- mice were stained with anti-ERα antibodies. Representative sections are shown for mammary intra-epithelial neoplasias (MIN) and adenocarcinomas that differ in ERα status. The tissues from nulliparous mice include (i) ERα+ MIN, (ii) ERα- adenocarcinoma, and (iii) ERα+ adenocarcinoma. The tissues from parous mice include (iv) ERα- MIN, (v) ERα- adenocarcinoma, and (vi) ERα+ adenocarcinoma. Scale bar = 20 μm. ERα, estrogen receptor-alpha.