“…Moreover, there exists a wide variation in results among laboratories using the same method (Borjesson et al, 1987). There is a convention using 10 fmol mg-' cytosol protein to separate between ER-negative and ERpositive tumours (McGuire et al, 1975), although many institutions use lower (Stewart et al, 1982;Hartveit et al, 1983;Mason et al, 1983;Howat et al, 1985;Bonneterre et al, 1988) or sometimes higher (Vollenweider-Zerargui et al, 1986) values. There is greater assay variability for PR (Jordan et al, 1983) and here again the cut-off values are variable.…”