Estrogen Receptor and Cytokeratin 5 Are Reliable Markers to Separate Usual Ductal Hyperplasia From Atypical Ductal Hyperplasia and Low-Grade Ductal Carcinoma In Situ.

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-High-molecular weight cytokeratins, such as cytokeratin 5 (CK5), are helpful to distinguish usual ductal hyperplasia (UDH) from atypical ductal hyperplasia (ADH) or low-grade ductal carcinoma in situ (DCIS). Few studies have looked at combining CK5 with estrogen receptor (ER) to differentiate UDH from ADH. -To evaluate the expression pattern of CK5 and ER as single or combined markers to separate UDH from ADH and low-grade DCIS. -A total of 23 ADH, 10 low-grade DCIS, and 32 UDH whole-tissue slides were stained for ER, CK5, progesterone receptor (PR), and Bcl-2. Nuclear staining of ER and PR was scored as diffuse (>80%), focal (10%-80%), or negative (<10%). Cytoplasmic staining of CK5 and Bcl-2 was scored as diffuse (>60%), focal (10%-60%), or negative (<10%). Differences in staining patterns were evaluated. -For ER staining: 94% of ADH/DCIS cases showed a diffuse staining pattern, whereas none of the 32 UDH cases showed diffuse staining. For CK5 staining: 96% of ADH/DCIS cases were negative or focally positive, whereas all 32 UDH cases had diffuse staining. The combination of ER and CK5 increased the sensitivity (94% to 97%). For PR staining: 11 of 23 ADH cases (48%), 6 of 10 DCIS cases (60%), and 4 of 32 UDH cases (13%) showed diffuse staining. Bcl-2 staining showed no statistical significance (P = .73). -Although morphology remains the gold standard, ER and CK5 are useful makers to differentiate UDH from ADH. Progesterone receptor staining may have limited value, and Bcl-2 staining is not useful.