To elucidate the clinical importance of estrogen receptor (ER) ␤ in breast cancer, 29 archival primary breast cancer specimens, six locally recurrent cancers, and five benign mammary tumors were examined histochemically for ER␣, ER␤ and the proliferation markers Ki67 and cyclin A. In benign tumors, most epithelial cells contained ER␤, but ER␣ was rare. In primary cancers, both ER␣ and ER␤ occurred in epithelial cells, the presence of ER␤ being associated with elevated expression of Ki67 and cyclin A, and ER␣ with decreased levels. Thus, the highest content of proliferation markers was seen in primary cancers that were ER␣ ؊ ER␤ ؉ . Most Ki67-containing cells coexpressed ER␤, but few showed ER␣. In locally recurring cancers, ER␣, ER␤, and Ki67 were more highly expressed than in the corresponding primary tumors, and many cells containing ER␤, but few with ER␣, expressed Ki67. Surprisingly, ER␤, but not ER␣, was seen in the stromal cells of both primary and recurrent cancers. Because the response of breast cancers to tamoxifen therapy is correlated with the presence of ER␣, cancer cells that lack ER␣ but contain ER␤ and proliferation markers represent a novel population of apparently proliferating cells that probably are not targeted by the current antiestrogens. Thus, appropriate ER␤-specific ligands, perhaps in combination with tamoxifen, may be useful in improving the treatment of breast cancers.

Estrogen is essential for normal growth and differentiation in the mammary gland. It also supports growth of approximately 50% of primary breast cancers. For this reason, removal of estrogen or blocking of its action with the anti-estrogen, tamoxifen, is the main treatment for estrogen receptor alpha (ERα)-positive tumors. In 1996, when oncologists became aware of a second ER, ERβ, there was some doubt as to whether this receptor would be of importance in breast cancer because the clinical consensus was that responsiveness to tamoxifen is related to the presence of ERα in breast cancer. Today we know that ERα and ERβ have distinct cellular distributions, regulate separate sets of genes and can oppose each other's actions on some genes. We also know that ERβ is widely expressed in both the normal and malignant breast and that there are proliferating cells in the breast which express ERβ. In this review we summarize what is known about ERβ in breast cancer and examine the possibility that ERβ-selective ligands may well represent a useful class of pharmacological tools with a novel target, namely proliferating cells expressing ERβ.

The relationship between immunoreactivity for cell proliferation markers (Ki67 and PCNA) and the growth fraction as determined by the fraction of labelled mitoses method was assessed in xenograft tumours grown from the LoVo cell line in nude mice. FLM curves were constructed by injecting tritiated thymidine and then preparing autoradiographs from the tumours. From this data an estimate of growth fraction and cell cycle time were made. Using frozen material from the same tumours, the Ki67 index was determined by immunostaining. PCNA staining was determined in the fixed material which had been used for the autoradiographs. The results show that Ki67 staining follows the same trend as the FLM-determined growth fraction as the tumour increases in size and the rate of growth decreases. However the Ki67 index does produce a consistent overestimate of the growth fraction in this in-vivo system, as compared to observations in cell culture. PCNA staining showed virtually 100 per cent positive staining in all the tumours, which is likely to reflect the long half-life of the antigen, compared to the very fast cell-cycle time of the xenograft tumours. These results show that staining with proliferation markers is not a precise determinant of growth fraction. Ki67 staining is a method that can be usefully applied as an operational marker of cell proliferation, but should not be used uncritically. Further caution is necessary in the use of PCNA. The findings also demonstrate the need to use a range of methods when assessing a new proliferation marker.

The distributions of three novel peptides, 7B2, neuromedin B, and neuromedin U, in rat, mouse, and human pituitaries, rat hypothalamus, and 30 human pituitary tumors were investigated with immunocytochemistry. Immunoreactivity for 7B2 was present in rat, mouse, and human gonadotropes, in intermediate lobe cells and posterior lobe nerve fibers in rats and mice, in rat hypothalamus (particularly in the median eminence), and in eight human pituitary gonadotropinomas. In gonadectomized rats, larger, more numerous LH beta- and 7B2-immunoreactive gonadotropes were seen than in controls. Extractable 7B2-like immunoreactivity was elevated but not significantly so in gonadectomized rat pituitaries [males: castrated, 37.4 +/- 4.3 (mean +/- SE); controls, 26.9 +/- 4.3; females: ovariectomized, 27.2 +/- 2.7; controls, 19.1 +/- 2.2 pmol/gland]. Neuromedin B immunoreactivity was found in normal rat and mouse thyrotropes and weakly in "thyroidectomy" cells in hypothyroid rats, in which extractable pituitary neuromedin B was significantly depleted (thyroidectomized, 87.0 +/- 14.0; methimazole-treated, 82.0 +/- 11.4; control, 230.7 +/- 25.6 fmol/gland). Hyperthyroid rat pituitaries showed increased TSH beta and neuromedin B immunoreactivities and neuromedin B content (TRH-treated, 385.2 +/- 30.2; T4-treated, 352.6 +/- 20.2; control, 230.7 +/- 25.6 fmol/gland). Neuromedin U immunoreactivity occurred in corticotropes of all species, in rat and mouse intermediate lobe, and throughout the rat hypothalamus, with immunoreactive cell bodies in the arcuate nucleus. Neuromedin U-immunoreactive cells were present in six of six human pituitary and five of six human extrapituitary corticotropinomas. In adrenalectomized rats, corticotropes were larger and more numerous than in controls, but extractable anterior pituitary neuromedin U-like immunoreactivity was not raised (adrenalectomized, 3.30 +/- 0.45; control, 3.32 +/- 0.27 pmol/gland). Our findings suggest that 7B2, neuromedin B, and neuromedin U may be involved in pituitary function.

E‐cadherin is a calcium‐dependent cell–cell adhesion molecule expressed by melanocytes and responsible for their adhesion to keratinocytes in vitro. In this study, the expression of E‐cadherin and its associated cytoplasmic proteins α‐, β‐, and γ‐catenin was evaluated in melanocytic lesions by immunohistochemistry. E‐cadherin expression was evaluated in 70 malignant melanomas and the catenins in 35 of these specimens. Twenty benign melanocytic naevi were also evaluated for E‐cadherin and catenin expression. In normal epidermis, E‐cadherin/catenin immunostaining was localized at the intercellular borders. In melanomas, a differential loss of E‐cadherin expression was observed. Membranous E‐cadherin staining was absent in dermal nests of melanomas in their radial growth phase and in Clark level II and III lesions, whereas it was present in a high proportion of melanomas in their vertical growth phase, in Clark level IV and V lesions and in metastasizing melanomas. In contrast, superficial compartments of naevi showed membranous E‐cadherin immunoreactivity and junctional naevus cell nests displayed heterogeneous or diffuse cytoplasmic staining. Cytoplasmic α‐ and β‐catenin, but not γ‐catenin staining were detected in all benign and malignant lesions. These findings indicate that qualitative changes in the expression and cellular localization of E‐cadherin and of α‐, β‐, and γ‐catenin occur in melanocytic lesions and may reflect different stages in their progression. Copyright © 1998 John Wiley & Sons, Ltd.