[158] A Comparative Study of p16 Expression in Basal-Like Carcinoma and High-Grade Invasive Ductal Carcinoma of the Breast

OL Bohn, M Fuertes-Camilo, L Navarro, J Saldivar, S Sanchez-Sosa. Christus Muguerza UPAEP University Hospital/Hospital Angeles, Puebla, Mexico

Background: Basal-like carcinomas of the breast (BLCB) are one of the molecular subtypes determined by gene expression profiling. BLCB generally have a high mitotic index, are ER-/PR-/HER2- (“triple-negative breast cancer”), and show variable expression of CK 5/6, CK14, EGFR and CD117. p16^INK4a expression has been identified in HPV-related carcinomas of genital tract and oropharynx. Little is known about p16^INK4a and BLCB. The aim of this study was to determine p16^INK4a expression in a subset of BLCB and compare the results with a group of high-grade invasive ductal carcinoma (HG-IDC) of breast.
Design: Tissue microarrays (TMA) were constructed in triplicate including 18 HG-IDC and 18 BLCB. Whole tissue sections were also used for BLCB. Immunohistochemical (IHC) stains for ER, PR, HER2, CK5/6, CK14, EGFR, CD117 and p16 were performed. The slides were stained using DAKO autostainer. Positive and negative controls were applied.
Results: The IHC results are summarized in Table 1.

		BLCB	HG-IDC
p16	Positive	16 (89%)	10 (55.5%)
	Negative	2 (11%)	8 (44.5%)
CK5/6	Positive	17 (94.4%)	5 (28%)
	Negative	1 (5.6%)	13 (72%)
CK14	Positive	17 (94.4%)	3 (17%)
	Negative	1 (5.6%)	15 (83%)
EGFR	Positive	14 (78%)	2 (11%)
	Negative	4 (22%)	16 (89%)
CD117	Positive	13 (72%)	2 (11%)
	Negative	5 (28%)	16 (89%)
ER	Positive	0 (0%)	2 (11%)
	Negative	18 (100%)	16 (89%)
PR	Positive	0 (0%)	3 (17%)
	Negative	18 (100%)	15 (83%)
HER2	Positive	0 (0%)	3 (17%)
	Negative	18 (100%)	15 (83%)

All BLCB cases were ER-/PR-/HER2-. Seventeen BLCB were CK 5/6+/CK 14+; EGFR was positive in 14/18 BLCB and CD117 was expressed in 13/18 BLCB. Nuclear diffuse expression of p16^INK4a was seen in 16/18 (89%) BLCB, ranging from 80% to 100%; nuclear p16^INK4a staining was present in 10/18 (55.5%) HG-IDC, ranging from 5% to 100%.
Conclusions: Our study shows that p16^INK4a was highly expressed in the majority of BLCB (89%) in comparison to HG-IDC (55.5%). In triple-negative breast cancer cases with CK5/6 and CK14 co-expression, p16^INK4a may serve as an additional biomarker for identification of BLCB.
Category: Breast

Monday, March 22, 2010 1:00 PM

Poster Session II # 66, Monday Afternoon