When breast ultrasound finds a lump, it usually turns out to be a benign mass such as a fibroadenoma or a cyst. Still, a benign result alone does not mean that no further care is needed. Depending on the mass's shape, its margins and how fast it grows, a few cases need differential testing, and new masses can also form over time.
This column sets out the standards used for follow-up after a benign breast tumour is diagnosed, and how the testing interval is decided. In short, shape and the speed of change matter more than size in deciding how the mass is managed. On that basis, regular follow-up tests every 6 months to 1 year are recommended.
01
Is a large tumour a dangerous tumour?
Key point
The risk of a breast tumour is not judged by size alone. A mass that is wider than it is tall, with smooth margins, leans towards benign findings and is watched with follow-up, whereas a mass that is taller than it is wide or has irregular margins needs detailed differential testing.
On breast ultrasound, more weight is given to the shape of the lesion and how fast it changes over time than to its size alone. For example, a lesion measuring 2 centimetres that is a wide oval with clear, smooth margins is judged to be benign and watched with follow-up. If a lesion is taller than it is wide or its margins look irregular, detailed differential testing is needed instead.
Shape and growth speed also have to be checked. A benign mass rarely turns into cancer over time. However, a mass first seen as a fibroadenoma is sometimes identified during follow-up as a different kind of mass, such as a phyllodes tumour, so changes in growth speed should not be missed.
- Wide oval shape — the margins are clear and smooth, so the mass is classed as a shape where benign findings are more likely
- Taller than wide, or irregular margins — if the margins look blurred and jagged like a saw, detailed differential testing is needed
- Growth speed — rather than size itself, how fast the shape changes is the key factor in judging risk
02
How do a fibroadenoma and a phyllodes tumour differ?
Key point
A fibroadenoma is a mass whose cells are classified as entirely benign, whereas a phyllodes tumour ranges widely from benign to borderline and malignant, so the two are hard to tell apart at first. Even when they look similar in shape, changes need to be checked through follow-up.
A phyllodes tumour is a mass with a jagged, leaf-like shape. It differs at root from a fibroadenoma because it is classified as benign, borderline or malignant depending on how much its cells overgrow and divide. A fibroadenoma's cells are always found to be benign. A phyllodes tumour can spread quickly into the surrounding tissue even when its margins look clear, so two masses of the same shape can carry very different actual risk.
In its early stage a phyllodes tumour has distinct margins, so it is hard to tell apart from a fibroadenoma on ultrasound findings alone. Even when a mass has been judged to be a fibroadenoma, it is followed up at set intervals to watch its growth speed and changes in shape. The possibility of a new mass forming separately from the existing one is also checked.
- Fibroadenoma — a mass whose cells are found to be entirely benign, with little change in shape
- Phyllodes tumour — classified as benign, borderline or malignant depending on how much the cells overgrow
- Limits of early distinction — both masses can look clearly defined, so they are not easy to tell apart by shape alone
03
How often should follow-up tests be done?
Key point
After the first scan has confirmed the size and shape of the lesion, the next check is usually scheduled 6 months later, although depending on the shape it may be moved 1 to 3 months earlier than that. If changes are small and the lesion stays stable, care switches to 1 routine check-up a year.
As a 1st step, the initial breast ultrasound checks whether there is a lesion and looks at its size and shape. The next step is deciding when the next test should be. Generally the next test is scheduled for 6 months later. If the shape of the mass is closer to the kind that needs detailed differential testing, the interval may be adjusted so that the recheck comes about 1 to 3 months earlier than that.
When several rounds of follow-up confirm that the shape has not changed much and stays stable, care then switches to 1 routine check-up a year. This step-by-step care allows early detection and prompt medical action, so problems can be dealt with properly before they grow.
Doctor's view
How the doctor decides
Seeun Cho, Medical Director · Obstetrics & Gynecology Specialist
I explain while we look at the screen together
I do not just say briefly, 'There is a lump here,' and move on. I show the ultrasound screen directly and explain both the current findings and the plan ahead. For example: 'From its shape it looks like a fibroadenoma, but it can change over time. If its shape has changed when we check in 6 months, we will confirm its nature with a biopsy.'
I do not recommend removal straight away
I do not think the decision on whether to remove a mass can be made on the day the ultrasound is first seen. After a mass is found, I value a process of confirming its nature through follow-up or a biopsy. Based on that result, the treatment direction and the follow-up plan are then decided together.
I plan the next test date together with the patient
I do not leave patients to decide the timing of their next test on their own. If the shape is stable, I suggest the next appointment 6 months later. If I judge that detailed differential testing is needed, I suggest it 1 to 3 months earlier than that. I also plan the care that follows together with the patient, and when needed I give it a few days and ask again.
Summary
In summary
Most masses found in the breast turn out to be benign findings unrelated to cancer. Depending on shape and growth speed, however, a few cases need detailed differential testing, and new masses can form over time. For that reason, even after a benign result, patients need to make a habit of checking for changes with regular follow-up tests every 6 months to 1 year. If a change in size feels different from usual, or the next test date recommended after the first scan is coming up, seeing a doctor at that time is the safe way to manage it.
FAQ
Frequently asked questions
If a tumour is benign, is there really nothing to worry about?
Most benign tumours do not progress to cancer, and if there are no symptoms such as pain, they can be left in place. However, a mass may rarely have a shape that needs detailed differential testing, or a new mass may form, so follow-up tests at the set intervals are the safer course.
How soon should a follow-up test usually be done?
After the first test, checks are usually done at 6-month intervals, and depending on the shape the next check may be moved 1 to 3 months earlier. If there is little change and the mass stays stable, care then switches to 1 check-up a year.
Can a fibroadenoma and a phyllodes tumour be told apart straight away on ultrasound?
In its early stage a phyllodes tumour has distinct margins, so it is hard to tell apart from a fibroadenoma on ultrasound alone. Even when a mass is judged to be a fibroadenoma, changes in its shape and growth are followed up to confirm its nature again.
If the lump is small, is it safe to stop worrying?
The risk of a mass is usually judged by its shape, margins and growth speed rather than its size. Even a small mass may be classed as needing detailed differential testing if it is taller than it is wide or has irregular margins.