Aim: 

To elucidate the role of the G-protein coupled melatonin receptor 1 (MT1) in breast tumours, paraffin-embedded tissue sections from tumorous (Tu) and adjacent non-tumorous (NTu) tissue samples from 42 breast cancer patients of different tumour stage and grade were investigated for cellular levels and subcellular localization of the receptor.

Methods: 

A mAB directed against the 2^nd cytoplasmic domain of MT1 was applied in the immunohistochemistry and tissue sections were examined in a Zeiss Axioplan2 microscope. Based on the staining intensity and the percentage of positively stained epithelial cells, an immunoreactive score (IRS) ranging from 0-12 points was used to classify MT1 levels.

Results: 

MT1 staining was observed in 40/42 Tu and 38/42 NTu specimens. In 21/ 42 cases, the IRS for MT1 staining in the Tu exceeded that of the adjacent NTu. In 12/42 specimens, MT1 levels in the Tu were lower than in NTu sections. No difference was seen in 9/42 cases. Remarkably, the pattern of MT1 staining of cellular structures varied between Tu and NTu specimens. Membrane staining was predominant in 26/42 NTu, but only in 3/42 Tu samples, whereas cytoplasmic staining was apparent in 32/42 Tu but only in 10/42 NTu specimens. Additional staining of nuclear compartments was seen in 15/42 Tu and 10/42 NTu samples.

Conclusion: 

We show that MT1 is present in the majority of Tu and NTu specimens from breast cancer patients with primary untreated tumours. Whether an altered subcellular localization might influence the function of MT1 in breast cancer has to be elucidated.