Immunohistochemical profile of invasive lobular carcinoma of the breast: predominantly vimentin and p53 protein negative, cathepsin D and oestrogen receptor positive.

Vimentin, p53 protein and cathepsin D positivity were assessed by immunohistochemistry, and oestrogen receptor (ER) by an enzyme immunoassay, in invasive lobular carcinomas (LC) of the breast. While vimentin was positive in only 5% (3/57) and p53 protein was positive only in 3% (2/63), cathepsin D was expressed in 86% (48/56) and ER in 78% (25/32). Classical LC were negative for p53 protein and all except one were cathepsin D positive. These results are in contrast to invasive ductal breast carcinomas (DC), where the reported average incidence of vimentin and p53 protein is much higher (19% and 33% respectively) and that of cathepsin D and ER lower (63% and 67% respectively). Thus lack of expression of vimentin and lack of p53 positivity together with high incidence of expression of cathepsin D and ER are more often associated with lobular than with ductal differentiation of invasive breast cancer. The results show that LC, distinguished morphologically, can further be defined by its immunohistochemical profile. This in turn may point to underlying biological differences between LC and DC.