Phenotypic and molecular characterisation of breast ductal carcinoma in situ

Abstract

Background Ductal carcinoma in situ (DCIS) comprises more than 20% of screen-detected breast cancer cases. The current understanding of the biology and clinical behaviour of DCIS and prediction of its progression to invasive disease remains incomplete. Treatment modalities vary; however, in most cases it involves surgical excision with or without adjuvant radiotherapy and endocrine therapy. To date, predictors of DCIS progression are not well defined; therefore, the aim of the current study was to characterise a large cohort of DCIS with long term follow-up data and identify possible predictors of DCIS outcome. Patients and Methods In this study, 1,249 pure DCIS cases and a control group of 239 DCIS cases mixed with invasion were identified between 1987–2017. Collection of the clinicopathological, management and outcome data was performed. Cases were reviewed and representative tumour blocks were selected and retrieved. Tissue microarrays (TMAs) were constructed (776 pure DCIS and 239 DCIS mixed with invasion), followed by molecular characterisation of DCIS for oestrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2) and proliferation marker (Ki67), using immunohistochemistry (IHC) and chromogenic in situ hybridisation (CISH). Mining for biomarkers with potential prognostic and predictive values in DCIS was performed with the identification of thioredoxin interacting protein (TXNIP), aurora kinase A (AURKA), a targeting protein for Xenopus kinesin-like protein 2 (TPX2), and a non-receptor tyrosine kinase (SRC) and their expression was assessed in the TMA using IHC. In addition, whole tissue sections of DCIS were used to assess tumour infiltrating lymphocytes (TILs) as a component of the tumours’ microenvironment. Results Analysis of the clinicopathological data of the DCIS patients revealed a significant increase in incidence of screen-detected DCIS during the period of the study. This was associated with a significant increase in the rate of breast conserving surgery (BCS) and the use of adjuvant radiotherapy (RT), along with a marked decline in the rate of re-excisions and recurrence. Screen-detected DCIS, localised DCIS lesions, small tumour size and negative surgical margins were the contributing factors to the reduced rate of re-excisions. Large tumour size, high tumour grade, and no adjuvant radiotherapy were independent predictors of the development of ipsilateral local recurrence. Molecular characterisation of DCIS using ER, PR, HER2 and Ki67 revealed that the highest proportion (60%) of cases were of Luminal A subtype, however the lowest attribution (11%) was for HER2 positive (+) tumours. Tumours of HER2+, Luminal B/HER2+ and Triple Negative subtypes were of larger tumour size (>40mm), higher tumour grade, and more frequently treated with mastectomy. When the molecular classes were investigated against the development of local recurrence, HER2 positivity was associated with ipsilateral DCIS local recurrence. The assessment of the selected tissue marker panel with potential role in predicting DCIS progression revealed a significant difference in their protein expression between pure DCIS tumours and those associated with invasion. An association between low expression of TXNIP, and high expression of AURKA, TPX2 and SRC with the development of local recurrence was detected and that AURKA, TPX2 and SRC were predictors of invasive recurrence independent of other predictors of recurrence, including tumour size, grade, and radiotherapy. Analysis of tumour infiltrating lymphocytes (TILs) showed that the most reproducible and prognostically significant method of TILs evaluation in DCIS is the assessment of touching TILs (defined as lymphocytes touching or within one lymphocyte cell thickness from the DCIS basement membrane), and that dense TILs predicted the development of local recurrence. Conclusions The outcome of DCIS improved significantly during the period of the study. This study identified several predictors of DCIS progression. In addition to some clinical and pathological variables including tumour size, grade and radiotherapy use, expression of TXNIP, AURKA, TPX2 and SRC, together with TILs density were independent predictors of DCIS outcome. These variables can potentially be used in combination to refine the prognostic stratification of DCIS patients in routine practice