The expression of growth factors, such as transforming growth factor a (TGFa), amphiregulin (AR) and CRIPTO, a type-I tyrosine-kinase growth factor receptor (erbB-2), and a tumor-suppressor gene (p53). that have been implicated in the development and/or the progression of breast cancer, was evaluated by immunohistochemistry in I00 human primary infiltrating breast carcinomas (IBC). AR and CRIPTO imrnunoreactivity was also assessed in 55 human breast ductal carcinomas in situ (DCIS). Within the I00 IBC, 80,50,73, 17, and 34 tumors expressed moderate to high levels of TGFol, AR, CRIPTO, erb6-2, and p53 respectively. In addition, AR and CRIPTO immunoreactivity were found in I I and in 26 out of 55 DCIS respectively. In contrast, only 4, 3, and 2 out of 10 normal mammary-gland samples were weakly positive for TGFol, AR, and CRIPTO expression, respectively, whereas none was positive for erbB-2 or p53. Within the I00 IBC, expression of erb6-2 significantly correlated with high histologic and nuclear grading, with high growth fraction, and with estrogen-receptor(ER)-and progesterone-receptor(PgR)-negative tumors. A statistically rignificant correlation was also observed between p53 expression and high histologic grading, high growth fraction, and PgRnegative tumors. In contrast, no significant correlations were found between TGFol, AR, and CRIPTO imrnunoreactivity and various clinicopathological parameters, with the exception of a positive correlation between TGFa and ER expression. These data demonstrate that TGFol, AR, and CRIPTO expression are significantly increased in malignant mammary epithelium relative to normal epithelium. In particular, the differential expression of CRIPTO may serve as a potential tumor marker for breast carcinogenesis.