Protein & gene

Currently, all breast cancers should be tested for expression, or detectable effect, of the estrogen receptor (ER), progesterone receptor (PR) and HER2/neu proteins.

These tests are usually done by immunohistochemistry and are presented in a pathologist's report. The profile of expression of a given tumor helps predict its prognosis, or outlook, and helps an oncologist choose the most appropriate treatment. More genes and/or proteins may be tested in the future.

Grade Tumor

The histological grade of a breast cancer is determined by a pathologist under a microscope.

• A well-differentiated (low grade) tumor resembles normal tissue.
• A poorly differentiated (high grade) tumor is composed of disorganized cells and, therefore, does not look like normal tissue.
• Moderately differentiated (intermediate grade) tumors are somewhere in between.

Classification

Breast cancers are described along four different classification schemes, or groups, each based on different criteria and serving a different purpose:

• Pathology - Each tumor is classified by its histological (microscopic anatomy) appearance and other criteria.
• Grade of tumor - The histological grade of a tumor is determined by a pathologist under a microscope.
• Protein & gene expression status - Currently, all breast cancers should be tested for expression, or detectable effect, of the estrogen receptor (ER), progesterone receptor (PR) and HER2/neu proteins.
• Stage of a tumor - The currently accepted staging scheme for breast cancer is the TNM classification.

Introduction

Breast cancer is a cancer that starts in the cells of the breast in women and men. Worldwide, breast cancer is the second most common type of cancer after lung cancer (10.4% of all cancer incidence, both sexes counted) and the fifth most common cause of cancer death.

In 2004, breast cancer caused 519,000 deaths worldwide (7% of cancer deaths; almost 1% of all deaths). Breast cancer is about 100 times as frequent among women as among men, but survival rates are equal in both sexes.