A hypoechoic mass is a lump that looks darker than the surrounding fat on ultrasound; the word on its own is not a sign of cancer, and a fibroadenoma, the most common benign breast lump, is usually hypoechoic too [4, 5]. What matters more is the shape, edge and orientation of the lump and the BI-RADS number in the report: an oval lump with a smooth edge lying parallel to the skin is most often benign, while an irregular lump, one with a spiculated edge or one that is "taller than wide" is more suspicious and usually needs a biopsy [2, 11]. A fibroadenoma very rarely turns into cancer, and a simple cyst is harmless [4, 6, 9].
Key points
- Hypoechoic only means "darker than the surrounding fat" on ultrasound; many benign lumps are hypoechoic too [4, 5].
- An oval lump with a smooth edge, lying parallel to the skin, is benign in most cases; an irregular lump, one with a spiculated edge or one that is "taller than wide" is more suspicious [2].
- A fibroadenoma is the most common benign breast lump in young women and very rarely turns into cancer [1, 6].
- A simple cyst is a harmless sac filled with fluid; a cyst with a thick wall or a solid part should have a biopsy [9].
- The BI-RADS number sums up all these terms and sets the next step [11]: What does my BI-RADS score mean?
What is a hypoechoic breast mass?
On ultrasound, how bright or dark a lump looks is compared with the surrounding fat [5]. "Hypoechoic" means the lump is darker than fat; "anechoic" means completely black, which is usually fluid, as in a simple cyst; "isoechoic" means the same shade as fat; and "hyperechoic" means brighter than fat [4, 9].
A typical fibroadenoma, the most common benign breast lump, is also hypoechoic [4, 5]; so being hypoechoic says nothing on its own about whether a lump is dangerous. On the other hand, a lump that is evenly and very bright (hyperechoic) and has no suspicious features is almost always benign [3]. The radiologist puts together the shape, edge, orientation and other features of the lump to decide the BI-RADS number [2, 11].
| Term in the report | What it means | What it usually points to |
|---|---|---|
| Hypoechoic | Darker than the surrounding fat [5] | On its own it points neither to benign nor to malignant; a typical fibroadenoma is hypoechoic too [4, 5] |
| Anechoic | Completely black; usually fluid [9] | A simple cyst, which is benign [4, 9] |
| Oval | An elongated, oval shape | Mostly benign: in one study, more than 8 in every 10 oval lumps were benign [2] |
| Lobulated | Oval with one or more wavy indentations; added back in the 2025 version [4] | Slightly more suspicious than oval [11] |
| Irregular | Neither oval nor round | More suspicious: in one study, about 6 in every 10 irregular lumps were cancer [2] |
| Circumscribed (smooth or well-defined edge) | The edge of the lump is sharp and clear | Mostly benign: 9 in every 10 were benign [2] |
| Indistinct, angular, microlobulated or spiculated edge | A blurred edge, a sharp corner, small scallops, or fine lines radiating out [4] | Suspicious; a spiculated edge is the most suspicious: more than 8 in every 10 were cancer [2] |
| Parallel (wider than tall) | The lump is wider than it is tall and lies parallel to the skin [11] | Mostly benign [2, 11] |
| Non-parallel (taller than wide) | The lump is taller than it is wide [11] | Suspicious: about 7 in every 10 were cancer [2] |
| Posterior shadowing | The area behind the lump looks darker | Any amount of shadowing matters and should be checked [4] |
| Posterior enhancement | The area behind the lump looks brighter | Seen in cysts and some benign lumps [5, 9] |
| Mixed solid and cystic | Partly fluid and partly solid [4] | A biopsy is needed; in one study, nearly 1 in every 4 complex cysts was cancer [9] |
| Echogenic pseudocapsule | A thin bright rim around the lump [4] | Mostly points to a benign lump, such as a fibroadenoma [3, 4] |
| Echogenic rind | A thick, uneven bright band around the lump; added in the 2025 version [4] | Mostly points to cancer, but is also seen with damaged fatty tissue (fat necrosis) [4] |
| Non-mass lesion | An area that looks different but does not have the shape of a lump; added in the 2025 version [4] | Depends on its features; a linear or segmental pattern with calcium deposits or shadowing is suspicious [4] |
The figures in this table come from a study of lumps that had been biopsied and only show which way each term points; no single term is a diagnosis, and the BI-RADS number in your report matters more.
What is a fibroadenoma?
A fibroadenoma is a benign lump made of the glandular and connective tissue of the breast. It usually feels firm and round, moves easily under the fingers and does not hurt; sometimes it is too small to be felt [1]. It is the most common benign breast lump and is seen most often in women aged 15 to 35, although it can be found at any age [1, 6]. Most fibroadenomas grow for a while and then stay the same size after a few years [6]. They may get larger when oestrogen levels rise, for example in pregnancy or with hormone therapy, and smaller after the menopause [1].
How is it diagnosed? By examination and ultrasound. On ultrasound, a typical fibroadenoma is an oval lump with a smooth edge, lying parallel to the skin and darker than fat [4, 5]. If every feature is completely typical, especially in young women, it can be followed with imaging instead of a biopsy [3, 6]. If there is any doubt, a core needle biopsy is the best way to make the diagnosis [6].
Follow-up: usually an examination and ultrasound every 6 months, and once a year if it has stayed the same for 2 years. Women aged 40 and over also keep having mammograms on the screening schedule [6]. See At what age should I start mammograms?
Can a fibroadenoma become cancer?
A fibroadenoma itself very rarely becomes cancer; that is why regular follow-up of a fibroadenoma confirmed by biopsy is safe [6].
Another question is whether having a fibroadenoma raises the risk of breast cancer later on. In a large study, two thirds of the women, those who had a simple fibroadenoma and no family history of breast cancer, had no higher risk than other women [7]. The risk was higher in women with a complex fibroadenoma, other changes in the surrounding tissue or a family history [7]. Another large study showed that most of this extra risk is linked to those changes in the surrounding tissue, not to the complex fibroadenoma itself [8].
Phyllodes tumour: a rare lump that can look like a fibroadenoma but sometimes grows quickly. Most of these tumours are benign, but some are cancer; they are seen most often in women in their 40s [1]. Ultrasound and mammograms cannot tell it apart from a fibroadenoma, so a lump that grows quickly or is larger than 3 cm is removed [6].
What is a complex fibroadenoma?
"Complex" is a word the pathologist writes after looking at the biopsy under the microscope: it means the fibroadenoma also contains other changes, such as cysts, calcium deposits or a particular kind of growth of the glandular tissue [1, 7]. A complex fibroadenoma is also benign and is more common in older women [1]. In a large study, the risk of breast cancer later on was higher in these women, but this increase was mostly linked to other changes in the breast tissue [8]. Your doctor will plan your follow-up based on the pathology result, your family history and your age.
Does a fibroadenoma need surgery?
Most fibroadenomas do not need surgery and are simply followed up [6]. Removing the lump is recommended in these cases [6]:
- a lump that grows quickly
- a lump larger than 3 cm
- a lump whose BI-RADS number has gone up at follow-up
- when the biopsy shows abnormal cell changes (atypia) or a possible phyllodes tumour
The lump can be removed with open surgery; lumps smaller than 3 cm can sometimes be taken out under ultrasound guidance with a special needle that removes the tissue by suction, without a large cut [6].
Fibroadenoma and pregnancy; a hypoechoic mass while breastfeeding
In pregnancy, a fibroadenoma may grow larger under the effect of hormones [1]. In a study of lumps biopsied during pregnancy and breastfeeding, fibroadenomas were larger than in other women and sometimes looked more suspicious on ultrasound; most of the benign lumps in this period were breast infections or abscesses and fibroadenomas [10].
Breast cancer can also occur during pregnancy and breastfeeding, and it does not look very different on ultrasound from other times [10]. So show any new lump in this period to a doctor and do not put it down to milk or hormones. Ultrasound is the main test, and sometimes a needle biopsy is needed to be sure [10].
What is a breast cyst? Simple and complex cysts
A breast cyst is a closed sac in the breast that is most often filled with fluid and is then called a "simple cyst". It may become painful before a period and is most common in women who have not yet reached the menopause or who take menopausal hormone therapy [1].
- Simple cyst: completely black on ultrasound, with a thin wall; it is benign (BI-RADS 2) and needs no treatment. If it is painful, the fluid can be drawn off with a needle [4, 9].
- Cyst with cloudy fluid (complicated cyst): its fluid contains fine particles. In one study, none of 38 cysts of this kind were cancer; it is usually followed up, and drained if it is painful [5, 9].
- Clustered microcysts: in the same study, all were benign [9].
- Complex cyst (complex cystic mass): it has a thick wall or thick internal walls, or a solid part can be seen inside; a biopsy is needed, because in the same study nearly 1 in every 4 was cancer [9].
Reports sometimes use the word "complex" for both of the last two types; if you are not sure which is meant, ask your doctor and look at the BI-RADS number in the report.
When should I see a doctor sooner?
Most hypoechoic lumps, fibroadenomas and cysts are harmless. But in these cases, do not wait for your next appointment:
- A lump that grows quickly, or is larger than 3 cm [1, 6]
- A lump that has changed, or whose BI-RADS number has gone up in a new report [6]
- A new lump during pregnancy or breastfeeding [10]
- A cyst with a solid part or a thick wall that has not yet had a biopsy [9]
Other signs that need prompt checking, such as changes in the skin or nipple, are listed in What are the symptoms of breast cancer?
Frequently asked questions
Does an irregular hypoechoic mass mean I have cancer?
Not necessarily, but an irregular shape is more suspicious and usually needs a biopsy. In a study of lumps that had been biopsied, about 6 in every 10 irregular lumps were cancer and the rest were benign [2]. See Does a biopsy make cancer spread?
What is an oval, well-defined hypoechoic mass?
Does a fibroadenoma go away on its own?
Does mastitis or a breast abscess also look hypoechoic on ultrasound?
Infection and abscess of the breast, especially during breastfeeding, are common causes of a lump and sometimes look suspicious on ultrasound; a biopsy is sometimes needed to tell them apart from cancer [10]. For redness and breast pain, see Does breast cancer hurt?
What does architectural distortion on a mammogram mean?
It means the normal structure of the breast tissue looks disrupted or pulled in at one spot, without a clear lump [11]. It may be caused by a benign lesion that looks like a scar (a radial scar), another benign tissue change (sclerosing adenosis) or cancer [11]. In studies, about 1 in every 3 distortions seen only on 3D mammography (tomosynthesis) was cancer, so a biopsy is usually recommended [12].
What does an asymmetry on a mammogram mean? Why was I called back?
Notes for doctors (for physicians)
For physicians
Predictive values of ultrasound descriptors. Hong 2005: 403 solid masses with known histology (35% malignant); PPV for malignancy: spiculated margin 86% (19/22), irregular shape 62% (102/164) and nonparallel orientation 69% (75/109); NPV: circumscribed margin 90% (160/178), parallel orientation 78% (228/294) and oval shape 84% (200/237) [2]. Stavros 1995: 750 solid nodules; benign criteria = absence of any malignant feature plus intense homogeneous hyperechogenicity, or a thin echogenic pseudocapsule with an ellipsoid shape or fewer than four gentle lobulations; 424 benign lesions were correctly classified as benign, and only 2 lesions classified as benign proved malignant at biopsy (NPV 99.5%, sensitivity 98.4%) [3].
Ultrasound lexicon in BI-RADS v2025. Lobulated shape added; "not parallel" and "not circumscribed" changed to "non-parallel" and "non-circumscribed"; "complex cystic and solid" renamed "mixed solid and cystic"; the combined posterior pattern removed (any degree of shadowing is considered significant); "non-mass lesion", "echogenic rind" and "echogenic pseudocapsule" added; a simple cyst confirmed on concurrent ultrasound moves an oval circumscribed mammographic mass to category 2 [4]. Lobulated is ranked slightly more suspicious than oval [11].
Cystic lesions (Berg 2003, 150 lesions with tissue diagnosis). 38 complicated cysts and 16 clustered microcysts: no malignancy; thick wall or septations (0.5 mm or more): 7 of 23 malignant; intracystic or mixed masses (at least 50% cystic): 4 of 18; predominantly solid masses with eccentric cystic foci: 7 of 38; overall 18 of 79 complex cystic lesions malignant. Symptomatic complicated cysts generally warrant aspiration [9].
Fibroadenoma and cancer risk. Dupont 1994 (1,835 patients): RR of invasive cancer 2.17 (1.5-3.2); complex fibroadenoma (cysts, sclerosing adenosis, epithelial calcifications or papillary apocrine change) 3.10 (1.9-5.1); proliferative disease in the adjacent parenchyma 3.88 (2.1-7.3); complex with a family history 3.72 (1.4-10); two thirds of patients (noncomplex and no family history) had no increased risk [7]. Nassar 2015 (Mayo, 2,136 women): SIR for noncomplex fibroadenoma 1.49 (1.26-1.74) and complex 2.27 (1.63-3.10); after stratification by involution status and PDWA, complex fibroadenoma was not an independent risk marker [8].
Management (CSBrS 2021). Core needle biopsy is the first choice for diagnosis; non-surgical follow-up for category 3 and for sonographically typical fibroadenomas in young patients, with examination and ultrasound every 6 months and every 12 months after 2 years of stability. Indications for surgery: rapid growth (volume increase of 16% or more per month under 50, 13% or more per month at 50 and over, or a mean change in dimension of more than 20% over 6 months), size over 3 cm, an increase in BI-RADS category, and atypia or suspected phyllodes tumour on core biopsy. Options: open excision, or ultrasound-guided VABB for lesions of 3 cm or less. Phyllodes tumours cannot be distinguished from fibroadenoma on ultrasound or mammography, and core biopsy may underestimate them [6].
Pregnancy and lactation (Qian 2019). 206 pathologically confirmed lesions in 195 patients: 51 malignant (50 IDC and 1 phyllodes tumour of low malignant potential) and 155 benign lesions (103 mastitis or abscess, 45 fibroadenomas); fibroadenomas were larger than in controls of childbearing age, and fibroadenomas and mastitis/abscesses had higher BI-RADS categories; the ultrasound appearance of cancer did not differ much, and ultrasound-guided core biopsy was needed to tell benign from malignant [10].
Architectural distortion and asymmetry. Meta-analysis of 14 cohorts (1,361 DBT-only AD lesions): malignancy 37% (95% CI 26-48), benign 41%, non-benign (malignant + high-risk) 59%; conclusion: biopsy rather than short-interval follow-up [12]. Focal asymmetry: PPV 7.4%-12.8% at screening and 19.7%-26.7% in the diagnostic setting; v2025 discontinued the descriptor "developing asymmetry", but a new or increasing focal asymmetry remains an indication for biopsy [11].
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