PUBLISHED ON: 14 October 2014

How do you define something? By definition, a definition is a statement of the meaning of a word.  Breast cancer is defined as such because it arises from cells within the breast tissue.  But when a disease like breast cancer is left to grow and develop it eventually spreads to other organs, forming tumours within the new tissue.  If breast cancer results in tumours forming on the liver, is this still breast cancer? Or should it now be defined as liver cancer? Breakthrough’s Dr Matthew Lam aims to answer some of these questions.

When breast cancer spreads away from the breast tissue and invades other organs, it is called secondary breast cancer.  This stage of the disease can be attributed to all deaths from breast cancer, yet it is surprising not only how little we know about it biologically, but also how little awareness there is of it.  Yesterday (13 October) was Secondary Breast Cancer Awareness Day. We recently undertook a survey in collaboration with YouGov which revealed that 55% of respondents did not know what secondary breast is. So what exactly is secondary breast cancer and how did it get its name?

The story of life

Breast cancer begins its existence from a single cell within the breast tissue.  This cell has been exposed to a plethora of pressures and events which have left some of the 3 billion pairs of ’letters’ which make up DNA damaged and muddled.  Like pages of a book being read out of place the story of life told by the genetic code no longer makes complete sense and as a result the cell begins to behave strangely.

The cell, which would normally only grow and split into new cells when told to, begins to multiply out of control.  Each new cell is a ‘clone’ of the original, harbouring the same faults.  These faults make the cell’s DNA unstable so as they divide they are at risk of muddling up even more ‘letters’ - pulling the story of life further and further away from the original draft.  These cells are now a tumour, a huddle of faulty cells mingled with healthy cells, recruited to provide support and nourishment for the greedy cancer cells.  This is primary breast cancer – the first or original tumour born out of the breast tissue.

The great escape

As the disease progresses, cancer cells from the primary tumour will eventually find their way into the blood stream, hijacking the transport system to spread to other parts of the body where they can form new tumours.  The development of a tumour at another organ is called a secondary cancer.  A tumour forming on an organ which was seeded by a cancer cell escaping from the primary breast tumour is a secondary breast cancer.  These new tumours are still defined as ‘breast cancer’ because the cells that form the tumour are breast cells.  The tumour may be in the liver but the cells comprising it are not liver cells.

Looking for the answers

Science has yet to unravel exactly how cancer cells spread to other parts of the body.  We need to understand more about this process, in particular, the differences between cancer cells in a secondary tumour versus a primary tumour.  Additional alterations to the story of life, written out in the genetic code of the cancer cells, continue to occur in secondary tumours.  This means treatments, which may have worked on the primary tumour, no longer work on the secondary.  If we are to prevent people dying from breast cancer, we are going to have to find the answer to these problems, and find a way to improve treatment options for patients with secondary breast cancer.

Dr Matthew Lam is Breakthrough Breast Cancer’s Senior Research Officer