p53
Several studies using antibodies to detect p53 protein indicate that p53 mutations are rare in benign lesions (Bartek et al., 1990; Heyderman and Dagg, 1991; Barbareschi et al., 1992; Eriksson et al., 1994; Stephenson et al., 1994; Umekita et al., 1994; Schmitt et al., 1995; Younes et al., 1995; Chitemerere et al., 1996; Siziopikou et al., 1996).

The total incidence of staining in these combined studies was 47/646 for benign lesions but most studies included fibroadenomas, which are frequently positive (Younes et al., 1995), as well as hyperplasias. In studies of hyperplastic lesions, only two of 80 specimens (2.5%) of PDWA and one of 108 atypical hyperplastic lesions were positive (Heyderman and Dagg, 1991; Umekita et al., 1994; Schmitt et al., 1995; Siziopikou et al., 1996).

DCIS is more frequently positive, with a total of 58 of 300 lesions staining for p53 (Bartek et al., 1990; Eriksson etal., 1994; Umekita etal., 1994; Leal etal., 1995; Schmitt etal., 1995; Chitemerere et al., 1996; Albonico et al., 1996; Siziopikou et al., 1996), and the proportion of invasive cancer-positive for p53 is higher yet; a total of 180 of 734 in total from a number of studies (Bartek et al., 1990; Heyderman and Dagg, 1991; Eriksson et al., 1994; Seth et al., 1994; Stephenson et al, 1994; Umekita et al., 1994; Younes et al., 1995; Nakopoulou et al., 1996). Seth et al. (1994) revealed that benign lesions, previously removed from two patients with p53-positive invasive cancers, were negative for p53.

The fact that CIS and carcinoma are similar inp53 expression but that hyperplastic lesions are rarely positive suggest ihaipSS mutation, like erbB-2, is not an early event in breast disease.

myc

C-myc is amplified in about 20% of breast cancers (Garcia et al., 1989; Berns et al., 1992). Interestingly, only 1% of cases are positive for both erbB-2 and c-myc (Garcia et al., 1989; Berns et al., 1992), again indicating at least two distict molecular pathways to cancer. Although erbB-2 amplification is a useful prognostic factor for ER-negative cases, c-myc amplification is a useful prognostic factor for ER⁺ cases (Berns et al., 1992). Unlike erbB-2, c-myc amplification occurs early in proliferative breast disease (Agnantisetal., 1992;Escotetal., 1993;Hehiretal., 1993; Pechoux et al., 1994; Brem et al., 1977).

Myc expression is induced by estrogen and appears to be hyper-responsive in atypical hyperplasia in that expression is very high during the follicular phase, but not the luteal phase, of the menstrual cycle in atypical hyperplasia relative to other benign lesions (Escot et al., 1993). This study also found that myc expression was significantly higher in benign lesions of patients with a first-degree family history of breast cancer.

C-myc amplification alters the reponse of breast epithelial cells to growth factors. EGF and FGF, which are normally mitogenic, transform cells that overexpress c-myc (reviewed in Dickson et al., 1992). Overexpression of c-myc in benign breast lesions may identify a high-risk subset as suggested by a finding of Hehir and colleagues: 62% of benign lesions from patients subsequently developing breast cancer were c-myc-positive, compared to 13% from patients who remained cancer-free. (1993).

Cyclin D1/PRAD1
Cyclin D1/PRAD1 is a cell cycle regulator necessary for Gl progression. The protein is overexpressed in one-third to one-half of invasive breast cancers as detected by immunohistochemistry (Bartkova et al., 1994, 1995; Zhang et al., 1994; Mcintosh et al., 1995; Zukerberg et al., 1995). Overexpression appears to first occur at DCIS (Bartkova et al., 1995; Weinstat-Saslow et al., 1995) and, in 37 cases of mixed DCIS and invasive carcinoma, was concordant in both invasive and noninvasive components (Bartkova et al., 1995). Elevated levels of PRADl mRNA were detected by in situ hybridization in proliferative disease, but PDWA and atypical hyperplasia were similar (18% in both; Weinstat-Saslow et al., 1995). The latter study revealed elevated PRADl mRNA in 76% of noncomedo DCIS, 87% of comedo DCIS, and 83% of invasive cancer. Thus, overexpression of PRADl, like p53 and erbB2, is associated with rapid progression to the DCIS stage.