Frequency of oestrogen and progesterone receptor positivity by immunohistochemical analysis in 7016 breast carcinomas: correlation with patient age, assay sensitivity, threshold value, and mammographic screening

Aims-A routine immunohistochemical (IHC) assay is now commonly used for det ermining the oestrogen receptor (ER) and progesterone receptor (PR) status of women with breast cancer. To date, no large studies have been conducted that report the expected frequency of receptor positivity in relation to pa tient age and sensitivity of the IHC assay. Data on 7016 breast carcinomas from 71 laboratories were analysed to determine the frequency of receptor p ositivity and investigate possible causes of the observed variation in dete ction rates. Methods-Members of UK NEQAS-ICC (UK National External Quality Assessment Sc heme for Immune cytochemistry) provided data on the receptor status of case s routinely assayed in their departments over a period of two to 26 months between June 1996 and September 1998. Data on 7016 breast carcinomas were s tratified according to patient age and receptor status. Frequency of recept or positivity was correlated with IHC assay sensitivity, the threshold valu e used to determine receptor positivity, and the presence or absence of mam mographic screening in the hospitals or clinics served by the laboratories. Results-The highest proportion of receptor positive cases occurred in patie nts in the age ranges > 65 years for ER and 41-50 years for PR. There was a significant positive correlation between frequency of receptor positivity and the sensitivity of the IHC assay, for both ER (r(s) = 0.346: p = 0.019; two tailed) and PR (r(s) = 0.561; p = 0.003; two tailed). The mean frequen cy of receptor positivity for laboratories using the same 10% threshold val ue was 77% for ER (95% confidence interval (CI), 74% to 80%) in laboratorie s with high sensitivity and 72% (95% CI, 68% to 76%) for those with low ass ay sensitivity (p = 0.025). For PR, the mean frequency of receptor positivi ty for laboratories using the same 10% threshold value and having high assa y sensitivity was 63% (95% CI, 57% to 69%), and 51% (95% CI, 38% to 65%) fo r laboratories with assays of low sensitivity (p = 0.022). The mean frequen cy of ER positivity for laboratories serving hospitals and clinics where ma mmographic screening does and does not take place was 73.4% and 75.7%, resp ectively (p = 0.302; two tailed). Conclusions-Of the parameters investigated, patient age and IHC assay sensi tivity were found to be the main variables influencing the frequency of rec eptor positivity. We recommend the range of receptor values obtained by lab oratories achieving high assay sensitivity as a useful guide against which all laboratories can gauge their own results.