FAMILIAL BREAST CANCER IS DIFFERENT Nadia M. Mokhtar, Ph.D. and Ragaey R. Fahmy MD Department of pathology, Benha faculty of medicine Benha University a b s t r a c t Twenty-one breast cancer patients with positive family history werw examined for biological and pathological features and the presence of p53 protein to determine the cardinal features of familial breast cancer. P27 expression in non-metastasizing PTC was lower than normal thyroid tissue (P≤ 0.01) and higher than metastasizing PTC (P≤ 0.01), p53 immunoreactivity was present, faint (grade 1) in 2 cases (11%) and moderate (grade 2) in one case ( 5.5%) of non-metastasizing PTC, while 15 (83.5%) cases on non-metastasizing PTCs and all of metastasizing PTCs and normal thyroid tissue had no immunoreactivity for p53. There was no statistically significanct difference among all groups of immunoreactivity for p53. Expression of Bax in patients with PTC was more than normal thyroid tissue ( P≤ 0.01). However, non-metastasizing and metastasizing PTC was similar. The results indicate that the metastasizing PTC showed significantly low CD44 expression than the non-metastasizing PTC (p ≤ 0.05), also the metastasizing and non-metastasizing PTC showed significantly less CD44 expression than the normal tissue (p≤ 0.05). These findings indicate more genetic instability in familial breast cancer which can be used to estimate the probability that a carrier of p53 germline mutation may develop breast cancer at a given age. Research in Benha M.J. 13 (3)(1996) 545–556.