Breast Cancer - An Introduction

Cancer is a disease where the normal cellular regulators malfunction and instead of the cells dying off as programmed they continually divide without their normal control, accumulating into a mass (tumour).

As the tumour grows, it promotes the formation of blood vessels to bring in oxygen and nutrients, however these vessels are 'leaky' and can allow the cancer cells to leave the tumour site and travel through the blood stream and lymphatic system to other parts of the body.

This process is called metastasis.

It is thought that the majority of breast cancers develop as the end result of a continuum of change within the breast tissue as depicted below. These changes usually take many years to progress to invasive carcinoma, and many never progress that far.

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Invasive Breast Cancer

The majority of these arise in the breast ducts (70%) and are therefore known as ductal cancers (or NOS). About 20% of cancers develop in the glands at the ends of the ducts and are called lobular cancers. The remaining 10% are called special type cancers and are discussed later.

These two main types of breast cancer tend to behave in a similar fashion although lobular cancers are more often multifocal (more widespread throughout the breast rather than causing an obvious mass - thus accounting for the increased difficult in detection mammographically) and bilateral (in both breasts). The most important factors in determining how well the cancer will behave is thus not the tumour type but its prognostic features.

Prognostic Features

There are 3 major prognostic features, which can be combined into an index to give an indication of disease severity (the Nottingham Prognostic Index -NPI) although this must be interpreted with some caution as the index is a statistical value that cannot tell you how you will fare (only the average outcome for 100 women with identical disease). The pathology report will contain information on all of features.

  1. ymph node status (ie metastatic involvement)
  2. histological grade: I, II, III (low - intermediate - high)
  3. tumour size

There are also several minor prognostic features which include

  • oestrogen/progesterone receptor status (ER /PR)
  • tumour subtype (ductal, lobular, etc)
  • lymphovascular invasion - LVI (presence of tumour cells in the small vessels around the tumour, in transit to the lymphnodes)
  • HER2 (or c-erbB-2) gene amplification (the 'herceptin' gene)

Special Types Of Cancers

As mentioned previously, these account for about 10% of cancers. The majority are less aggressive than ductal cancers per se, with the notable exception of inflammatory carcinomas -

  • mucinous
  • tubular
  • cribriform
  • papillary
  • adenoid cystic
  • medullary
  • inflammatory

Whilst these tend to present as breast lumps, with the final diagnosis often only confirmed on histology, inflammatory carcinomas deserve special mention. Blockage of the skin lymphatic channels leads to swelling and redness and thus it can be mistaken for a breast infection.

Paget's disease, whilst not a special type of cancer, also presents in an unusual way with nipple crusting and bleeding and can be mistaken for eczema of the nipple. The underlying cause is either DCIS or an invasive carcinoma affecting the ducts behind the nipple.

Clinical Staging

There are 2 main staging systems -

  • TNM: (where T is for Tumour size, N is for lymph Node involvement and M is for Metastasis) which can be both a clinical & histological staging system. It is important as a way of accurately describing the tumour and, for example, allowing similar groups to be analysed to assess outcomes in treatment trials.
  • Manchester system: which is a clinical staging method describing whether or not the tumour is confined to the breast.