HER2 2+ Breast Cancer in Mexico, Central America and the Caribbean: Re-Testing Results by a Central Lab
OL Bohn, L Navarro, C Ayaquica, J Saldivar, S Sanchez-Sosa. UPAEP University Hospital, Puebla, Mexico
Background: Pathologists have a prophetic role in determining Trastuzumab use. Concordance studies between central and local laboratories in North America and Europe have shown high degree of discordance, mostly in 2+ equivocal cases. No data of HER2 quality assurance are available from Latin America and the Caribbean. We determine concordance HER2 IHC 2+ in invasive ductal breast carcinomas cases between 29 local laboratories (15 in Mexico, 10 in Central America and 4 in the Caribbean) and a central reference laboratory in Mexico. In local laboratories, HER2 2+ tumors range between 6 to 11% of the total of cases submitted for HER2 IHC testing.
Design: A total of 1,086 blocks were reviewed by the central laboratory, interpreted by the local laboratories as 2+. Thirty-seven blocks were excluded (no tissue, no tumor present in the block). All tumor specimens were retested by HER2 IHC (Hercep Test) using the DAKO scoring system and fluorescence in situ hybridization (FISH). International external quality assurance to the central laboratory was run by the UK National External Quality assessment scheme (UK-NEQAS).
Results: Concordance between local and central laboratories HER2 IHC 2+ was 29.08% (n=305). Among 1,049 tumors, 539 (51.38%) were re-classified by the central lab as 0/1+ and 205 (19.54%) as 3+.
Table 1. Re-testing IHC by central laboratory
|IHC||FISH NON-AMPLIFIED||FISH EQUIVOCAL||FISH AMPLIFIED||TOTAL|
HER2 gene amplification by FISH, performed by central lab (HER2/CEP17>2.2), was present in 124/1,049 (11.82%) of the cases that had been reported as 2+ in the local laboratories, and equivocal amplification (HER2/CEP17 1.8-2.2) was present in 26/1,049 (2.48%). Concordance between central IHC and central FISH ranged between 96.10% (0/1+) and 98.05% (3+).
Conclusions: Current HER2 concordance for IHC 2+ equivocal cases between local and central laboratories is low, and in agreement with ASCO/CAP guidelines, HER2 testing should be performed by high-volume reference laboratory.
Tuesday, March 10, 2009 9:30 AM
Poster Session III # 58, Tuesday Morning