Fatty acid synthase (FAS) is the key enzyme required for the conversion of dietary carbohydrates to fatty acids. Recent studies have demonstrated that high levels of FAS expression occur in a variety of cancers, including breast cancer. We evaluated 243 primary breast cancer patients in the period between 1989 and 1996. Immunohistochemical staining for FAS was performed on formaline-fixed, paraffin-embedded sections. FAS staining intensity was graded as low or high. The expression of FAS was high in 145 (60%) and low in 98 cases (40%). A weak correlation between FAS expression and nodal status was noted in premenopausal patients (p=0. 01). FAS was associated with estrogen receptor (p=0.0022) and progesterone receptor (p=0.0085) status. We found that a low expression of FAS was significantly related to a shorter disease-free survival (DFS) rate in estrogen receptor positive patients (p=0.024) and a similar trend was recognized in progesterone receptor positive patients (p=0.083). The low FAS group showed better DFS and OS in all but ER-/PgR- cases (p=0.011, 0.076). This study showed close correlations between immunohistochemical FAS expression and steroid hormone receptors in premenopausal patients. The use of FAS expression may increase the diagnostic utility of ER and PgR in premenopausal patients. FAS may be able to predict the responsiveness of tumors to endocrine therapy.

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