Genome evolution in ductal carcinoma in situ: invasion of the clones

Abstract

Ductal carcinoma in situ (DCIS) is the most frequently diagnosed early-stage breast cancer. Only a subset of patients progress to invasive ductal carcinoma (IDC), and this presents a formidable clinical challenge for determining which patients to treat aggressively and which patients to monitor without therapeutic intervention. Understanding the molecular and genomic basis of invasion has been difficult to study in DCIS cancers due to several technical obstacles, including low tumour cellularity, lack of fresh-frozen tissues, and intratumour heterogeneity. In this review, we discuss the role of intratumour heterogeneity in the progression of DCIS to IDC in the context of three evolutionary models: independent lineages, evolutionary bottlenecks, and multiclonal invasion. We examine the evidence in support of these models and their relevance to the diagnosis and treatment of patients with DCIS. We also discuss how emerging technologies, such as single-cell sequencing, STAR-FISH, and imaging mass spectrometry, are likely to provide new insights into the evolution of this enigmatic disease. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Keywords: DCIS; breast cancer; breast cancer genomics; ductal carcinoma in situ; intratumour heterogeneity; next-generation sequencing; single-cell sequencing.

Figure 1. Progression of breast cancer and the histopathology of DCIS

(A) Progressive stages of high-grade breast cancer as defined by histopathology (B–E) H&E stained tissue sections of low-grade and high-grade DCIS at 200× magnification: (B) low to intermediate grade cribriform type DCIS, (C) cross section of a duct involved by high grade solid type DCIS, (D–E) synchronous high grade DCIS and IDC with evidence of microinvasion.

Figure 2. Evolutionary models of invasion in DCIS

(A) Independent Evolution Model shows the in situ and invasive subpopulations evolving from independent lineages that originated from two different normal cells (N₁, N₂) in the breast. (B) Evolutionary Bottleneck Model shows the evolution of three clonal subpopulations from a single ancestral (N₁), from which a single clone is selected during invasion and expands to form the invasive carcinoma. (C) Multiclonal Invasion Model shows the evolution of three clonal subpopulations from a single normal cell (N₁), in the breast. In this model all three clones escape the duct and co-migrate into the adjacent tissues to establish the invasive carcinoma.

Figure 3. Emerging technologies for investigating DCIS progression

(A) Laser-Capture-Microdissection and single cell DNA sequencing to perform spatially resolved genomic profiling of individual tumour cells. (B) STAR-FISH profiling of targeted mutations in tissue sections. (C) Imaging CyTOF can perform proteomic analysis of up to one hundred proteins in thousands of single cells in tissue sections, while preserving their spatial context and organization.