H&E (Haemotoxylin and Eosin) : H&E staining is the most commonly used technique to visualize the tissue biopsy sections. H&E technique uses two different types of dye; one stains to the DNA in the nucleus of the cell (purple color) whereas the other stains the cytoplasm (parts of cell outside the nucleus) (pink color). H&E stained tissue slides are generally used for quality control purposes so as to assure that the tissue biopsy and FFPE preparation is correctly carried out.
H&E staining technique gives a very detailed view of the tissue. It helps visualize (under microscope) different cells and structures within a tissue gives a sense of the overall condition of the tissue under examination. This information is often sufficient to allow a disease diagnosis based on the organization (or disorganization) of the cells and also shows any abnormalities or particular indicators in the actual cells (such as nuclear changes typically seen in cancer). The pathologist studies the tissue morphology in these slides to assess the following
- If the biopsy tissue sample is benign (non-cancerous) or malignant (cancerous)
- If the biopsy is malignant, the pathologist also assigns the tumor grade (i.e. pathological staging) based on the histological examination (Grade 1, 2, 3, or 4; in the increasing order of aggressiveness). These tumor grade could potentially serve as one of the clinical-data features in the machine learning algorithm for tissue classification. Note that pathological staging is different that clinical staging.
- The pathologist also determines if the tumor has likely metastasized (i.e. spread to other parts of the body). The pathologist may ask for more biopsy test if need.
Specifically, the pathologist considers the following factors while making the above inferences.
- Tumor size
- Tumor Spread: (a) within the breast (lymphovascular invasion), (b) to nearby lymph nodes, or (c) to distant sites (e.g. lungs, brain, etc)
- Adequacy of surgical removal (Marginal Status): distance between the cancerous and normal (non-cancerous) tissue within the breast
- Tumor grading: Gland formation, Nuclear morphology, Mitosis rate
- Histopathological subtype classification of breast cancer (growth pattern): [Note: Histopathological subtype of breast cancer is completely different to the Molecular subtype of beast cancer. More details on sections below.]
Histopathological subtype classification of breast cancer
This is a traditional way of classifying the breast cancer based on the histopathology of the breast. Although, these days breast cancer are classified by their molecular subtype, pathologist often tend to perform this classification anyhow. Based on the tissue morphology and where on the breast tissue a cancer is detected, breast cancer are classified as follows.