Prohibitin expression is associated with high grade breast cancer but is not a driver of amplification at 17q21.33

Abstract

Aims: In a study of ductal carcinoma in situ of the breast, we identified five genes at chromosome 17q21.33 that were over-expressed in high grade cases, and showed a correlation between expression and gene copy number. The aim of this study was to investigate potential drivers of genomic amplification at 17q21.33.

Methods: Analysis of high resolution comparative genomic hybridisation and published data specified a minimum region of amplification at 17q21.33. Prohibitin (PHB) expression was examined by immunohistochemistry in 285 invasive breast cancers. Gene copy number was examined by fluorescence in situ hybridisation.

Results: The minimum region of amplification at 17q21.33 included ten genes with PHB selected as a candidate driver. Increased PHB expression was associated with higher grade breast cancer and poorer survival. Amplification of PHB was detected in 13 of 235 cases (5.5%) but was not associated with PHB expression. PHB amplification was most common in the ERBB2+ breast cancer subtype, although high expression was most prevalent in basal-like and luminal B cancers.

Conclusions: Amplification at 17q21.33 is a recurrent feature of breast cancer that forms part of a 'firestorm' pattern of genomic aberration. PHB is not a driver of amplification, however PHB may contribute to high grade breast cancer.

Fig. 1

(A) High resolution CGH mapping of 17q in ERBB2 amplified (n = 9) and non-amplified (n = 7) in situ carcinoma samples. Four samples showed a region of amplification at 17q21.33. (B) Genes included in the 17q21.33 amplicon. (C) Genes included in the same 17q21.33 region from the high resolution CGH study of Haverty et al. (D) Ten genes included in the minimum region of overlap in amplification at 17q21.33 in eight cases.

Fig. 2

(A–C) Examples of low, intermediate and high level immunohistochemical staining of invasive breast cancers for PHB. (D) Kaplan–Meier survival curve demonstrating better cancer specific survival associated with negative/low level PHB expression compared with moderate and high level expression in invasive breast cancer (n = 285; p = 0.039).

Fig. 3

(A–F) FISH showing a 17q21.33 probe including PHB (green) relative to a chromosome 17 centromeric probe (red). (A,B) Invasive breast cancers from the tissue microarray cohort. (C,D) An amplified and un-amplified case included in the high resolution CGH study. (E,F) 17q21.33 amplified BT474 and unamplified MCF7 breast cancer cells. (G) The relationship between PHB FISH ratio and PHB immunohistochemical score in invasive breast cancer (n = 233; p = 0.154).