Mapping tumour tissue: quantitative maps of histological whole slide images

Abstract

Immunohistochemistry (IHC) is the standard method to assess tumour tissue on a micro-scopic scale. IHC selectively highlights microscopic structures in the tissue and yields quantitative information that can be used to answer questions like:“How many immune cells are present in a given tumour?”,“How many tumour cells are actively proliferating?”, or “How many blood vessels are present in the tumour?”. These questions are addressed by histopathologists who visually observe regions of immunostained slides of tumour tissue and count structures of interest, for instance, cells or blood vessels. In the clinic, this quantitative information can be then used to estimate the prognosis of a patient. For example, the number of blood vessels in tumour tissue is a prognostic factor for colorectal cancer patients [1]. Pathologists combine the excellent human vision and pattern recognition skills of the brain with an extensive training in tissue observation. Traditionally, pathologists use only a microscope to identify and assess structures of interest manually. However, the limitations of manual procedures are evident; besides the possibility of human error, the dimensions of tissue slides in high magnification are huge and it is not feasible to view the whole slide nor manually visualise or count any objects of interest. Therefore, microscopic structures such as blood vessels are only quantified in a small fraction of the entire tumour image [2]. However, tumour tissue is highly heterogeneous and adjacent tumour tissue areas may have very different properties [3]. This reflects a problem in traditional histopathology: if we only quantify objects in a small part of the whole.