Radioimmunoassayable insulin-like growth factor-I in human breast cyst fluid

insulin-like growth factor-I (IGF-I) was measured in breast cyst fluid and serum collected at the same time. In addition, epidermal growth factor (EGF) was measured in breast cyst fluid. The radioimmunoassay inhibition curve of cystic IGF-I was parallel to that of authentic IFG-I. Cystic immunoreactive IGF-I had an elution pattern similar to IGF-I from Sep-Pak C18 silica columns and from gel-filtration chromatography using Sephacryl 200. The material from Sephacryl 200 gave a radioimmunoassay curve which was parallel to IGF-I. The median (range) amount of IGF-I in cyst fluid was 9.3 ng/ml (0.8-33.3 ng/ml) and was 5-10% of that found in serum, although there was no significant correlation between the two levels. The median (range) level of cystic EGF was 416 ng/ml (14-1640 ng/ml). There was a weak negative correlation between cystic EGF and cystic IGF-I (P less than 0.01). Some women presented with multiple cysts and for these cysts there was a high degree of concordance of levels for both IGF-I or EGF. Unlike serum there was little or no protein present in cyst fluid which bound IGF-I.