Can a cyst found in my breast ultrasound turn cancerous?

All simple cysts, which are cysts that do not have any solid mass associated with them, are benign, with no risk of future cancer.

Q: I am 39 years old and just went for an annual health screening.

The ultrasound report for my breasts said: "A cyst is seen at the 7o'clock position in the right breast measuring 3mm in diameter. The lesion is oval and well marginated. A small 3mm benign cyst is seen in the right breast."

How accurate is it to conclude that the cyst is benign just by looking at it? If it is benign, can it turn cancerous later? When should I schedule my next breast check?

A: A cyst is a collection of fluid within a sac in the breast tissue, which is very different from a solid lump.

All simple cysts, which are cysts that do not have any solid mass associated with them, are benign, with no risk of future cancer.

They tend to come and go, especially if they are less than 10mm in diameter.

Cysts may occasionally get bigger - up to a third of cases behave this way. Such a cyst can be felt as a lump in the breast, that may or may not be painful, depending on how tense the cyst is.

What most women notice is that there is initially some pain in the breast, and when they examine the area, there is a lump that was not there before.

Over the space of a few days to weeks, they may notice that the lump becomes less painful, less obvious to the touch, or appears to have become smaller. The size may fluctuate with the menstrual cycle.

It is occasionally hard to distinguish between a cancerous tumour and a cyst just by feeling it.

Most of the time, a cancerous tumour is usually described as being rock hard, while a cyst is a little bit fluctuant - which means that when you press down on a cyst, you can feel it give way a bit under pressure, whereas a cancerous tumour will not give way at all under pressure.

But some cysts - because they are full of fluid - can feel as hard as cancerous tumours.

Ultrasound scans are extremely accurate in distinguishing between solid and "fluid-filled" lumps in the breast.

Cancerous tumours are solid, tend to have irregular margins and spiculated (with spikes or points on the surface) shapes. Cysts tend to be spherical or oval, and each has a thin-walled sac that can be seen.

What is of concern when assessing cysts is whether there are solid growths associated with the cysts - these are potentially serious and a biopsy (test of a sample of cells) should always be performed to establish the diagnosis.

Cysts can be left alone but if they are causing pain, the fluid can be extracted. Please consult your doctor if you feel any pain or discomfort.

You do not need repeat scans for the cyst. You only need to begin normal screening for breast cancer - in the form of annual mammograms - at the age of 40.

Dr Chan Ching Wan
Consultant at the division of general surgery (breast surgery) at the National University Hospital


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