Involucrin expression in breast carcinomas: an immunohistochemical study

Brk/PTK6 and Involucrin Expression May Predict Breast Cancer Cell Responses to Vitamin D3

The process of human embryonic mammary development gives rise to the structures in which mammary cells share a developmental lineage with skin epithelial cells such as keratinocytes. As some breast carcinomas have previously been shown to express high levels of involucrin, a marker of keratinocyte differentiation, we hypothesised that some breast tumours may de-differentiate to a keratinocyte-derived 'evolutionary history'. To confirm our hypothesis, we investigated the frequency of involucrin expression along with that of Brk, a tyrosine kinase expressed in up to 86% of breast carcinomas whose normal expression patterns are restricted to differentiating epithelial cells, most notably those in the skin (keratinocytes) and the gastrointestinal tract. We found that involucrin, a keratinocyte differentiation marker, was expressed in a high proportion (78%) of breast carcinoma samples and cell lines. Interestingly, tumour samples found to express high levels of involucrin were also shown to express Brk. 1,25-dihydroxyvitamin D3, a known differentiation agent and potential anti-cancer agent, decreased proliferation in the breast cancer cell lines that expressed both involucrin and Brk, whereas the Brk/involucrin negative cell lines tested were less susceptible. In addition, responses to 1,25-dihydroxyvitamin D3 were not correlated with vitamin D receptor expression. These data contribute to the growing body of evidence suggesting that cellular responses to 1,25-dihydroxyvitamin D3 are potentially independent of vitamin D receptor status and provide an insight into potential markers, such as Brk and/or involucrin that could predict therapeutic responses to 1,25-dihydroxyvitamin D3.

Squamoid features and expression of involucrin in primary breast carcinoma associated with high histological grade, tumour cell necrosis and recurrence sites

Although breast carcinomas are considered to originate from glandular epithelial cells, some exhibit 'squamoid features', comprising stratification with a gradient in the nuclear-cytoplasmic ratio within individual cancer cell nests on microscopy. In parallel with a histological review of squamoid features, we immunohistochemically investigated the expression of involucrin, a marker of terminal squamous differentiation, in 223 breast carcinomas with one to three regional nodal metastases but no distant metastases and analysed their association with other clinicopathological parameters to explore their clinical and biological implications. Squamoid features and involucrin expression, detected in 22% and 27% of cases respectively, correlated with each other and were associated with high-grade atypia, a solid-nest pattern, cancer cell necrosis on histology and negative oestrogen receptor status. The incidence of regional recurrences was higher in patients with involucrin expression, whereas bone metastases were less frequent in groups with squamoid features or with diffuse (> or = 10%) involucrin expression. Both squamoid features and involucrin expression, which were considered to be derived either from differentiation into keratinocytes or from some kind of cellular degeneration caused by high turnover rate, are suggested to influence the biological behaviour of breast cancer cells in vivo, and they may be effective in predicting the most likely recurrence sites.