Sentinel lymph node biopsy (SLNB) is currently used in the UK for axillary staging in breast cancer. Node localisation is achieved with the combination of injected dye and radioactive tracer.¹ The commonly used dyes are the isomers isosulphan blue and Patent blue V (PBV).^1–3 Methylene blue (MB) is also used in some centres as it is cheaper and easily available.⁴ In the Far East, other dyes such as Indigocarmine (IDC) are also being used.⁵

In the 1980s, when dyes were used to localise occult breast cancers before surgery, studies were carried out on the effect of the dyes on oestrogen receptor (ERα) assessment by ligand-binding assay. These showed a decrease in the binding capacity after treatment with MB but not with isosulphan blue.^6,7 Given the importance of the determination of ERα expression in the treatment of breast cancer and the wider use of SLNB to stage the axilla, we investigated whether the dyes used change the immunocytochemical profile of these receptors.

Materials and methods

The ERα-positive and progesterone receptor (PR)-positive malignant breast cell line MCF-7 was cultured under standard conditions and exposed to the dyes diluted 1:10, 1:100 and 1:1000 in triplicate for 4 and 24 h. The dyes used were 2.5% PBV (Guerbert, France), 1% MB (Martindale Pharmaceuticals, UK) and 4% IDC (Amino), which are the concentrations used clinically for …