What Is a Breast Papilloma? Diagnosis, Risk, & Treatment

A breast papilloma is a benign (noncancerous) growth that forms inside a milk duct of the breast. It develops when the cells lining a duct proliferate into a small, finger-like or wart-like projection, usually attached to the duct wall by a thin stalk. Most papillomas are harmless and treatable, but they draw clinical attention because they can mimic cancer on imaging, sometimes harbor hidden abnormal cells, and occasionally coexist with early-stage malignancy. The gap between “almost certainly benign” and “definitely benign” is where much of the debate around papillomas lives.

What a Papilloma Feels Like and How It Shows Up

The hallmark symptom is nipple discharge, often bloody or clear, coming from a single duct. In many cases the discharge is the only sign. Some people also notice a small, palpable lump near the nipple. A case report in BMJ Case Reports described a 32-year-old woman who presented with a 3 cm breast lump and bloody nipple discharge during early pregnancy, which turned out to be a benign papilloma.¹ Not everyone gets symptoms, though. Some papillomas are found incidentally on a mammogram or ultrasound done for another reason, appearing as a small mass or a dilated duct with something inside it.

Bloody nipple discharge understandably alarms people, but the vast majority of the time it points to a papilloma rather than cancer. Roughly 40 to 70 percent of pathological nipple discharge in women traces back to a papilloma.² That said, about 5 to 10 percent of people with blood-stained discharge turn out to have an underlying malignancy, so the symptom always warrants investigation.

Solitary Versus Multiple Papillomas

Papillomas fall into two broad categories based on where they grow and how many there are. A solitary (or “central”) papilloma typically sits in one of the large ducts just behind the nipple. It is usually a single growth in a premenopausal or perimenopausal woman and is the classic cause of spontaneous nipple discharge.

Multiple (or “peripheral”) papillomas grow farther from the nipple, in the smaller ducts of the breast. They tend to appear in clusters and are less likely to cause discharge but more likely to show up as a mass or an area of concern on imaging. The distinction matters for risk. A review in Surgical Clinics of North America found conflicting data on whether a solitary papilloma raises breast cancer risk, though the most recent series do find an elevated risk; multiple papillomas, on the other hand, are more clearly associated with both coexisting cancer and subsequent cancer development.³

How Papillomas Are Diagnosed

Diagnosing a papilloma usually involves a combination of imaging and tissue sampling. Ultrasound is often the first step, especially when a patient has nipple discharge. On ultrasound, a papilloma typically appears as a solid mass inside a dilated duct, sometimes with a visible stalk. In adolescents and younger patients the finding is rare but does occur; one reported case involved a teenage girl whose ultrasound showed a solid, oval-shaped mass in the subareolar region.⁴

MRI can add useful detail but also creates confusion, because papillomas frequently look suspicious on MRI. One study found that only a small fraction of papillomas showed the “classic benign” combination of a round or oval shape, smooth margins, and a gradually rising enhancement curve; most had features that scoring systems would flag for biopsy.⁵ Research comparing papillomas and invasive ductal carcinomas on MRI found that papillomas were more often round or oval (about 61 percent) and had smooth margins more frequently (about 43 percent) than cancers, but there was enough overlap that imaging alone cannot reliably distinguish the two.⁶ A study of 158 patients found that on MRI, masses larger than 10 mm and those showing a mixed mass-plus-non-mass-enhancement pattern were independent risk indicators for a papilloma harboring high-risk or malignant cells.⁷

Because imaging cannot give a definitive answer, tissue sampling is essential. A core needle biopsy is the standard first step, but there is a well-known limitation: the needle may not sample the most concerning part of the lesion, a problem called undersampling. Histopathology remains the gold standard, and the possibility of undersampling on percutaneous biopsy is a major reason the management of papillomas remains controversial.⁸

Nipple Discharge Cytology

When discharge is present, the fluid itself can be examined under a microscope. Cytology of the discharge detected abnormal cells in about 70 percent of papillomas and 92 percent of atypical or malignant lesions in one study, though the specificity was low at 30 percent, meaning the test frequently flagged benign conditions as suspicious.⁹ The cells and biomarkers in ductal fluid are also being explored as potential screening tools for high-risk patients, though that research is still in early stages.¹⁰

The Challenge of Telling Papillomas from Papillary Carcinomas

Under the microscope, the line between a benign papilloma and a papillary carcinoma can be surprisingly thin. Both lesions have finger-like projections of tissue, but they differ in the structure of those projections, the amount of supporting tissue within them, and the behavior of the lining cells. Fibrosis at the edge of a papilloma can trap glands and mimic invasion, and needle biopsies can deposit benign cell clusters in patterns that look invasive.¹¹ Laboratory markers can help: a study found that a surface protein called CD44s was expressed in all 11 papillomas tested but was absent or very low in 8 of 10 papillary carcinomas, making it a useful tool when the microscopic picture is ambiguous.¹²

The Upgrade Question

The central anxiety around papillomas is this: when a core needle biopsy says “benign papilloma,” how often does surgical removal reveal something worse? This is known as the upgrade rate, and it varies enormously depending on whether abnormal cells (atypia) are present.

A large meta-analysis pooling data across many studies found that the upgrade rate for benign papillomas without atypia was about 5 percent, while papillomas with atypia upgraded to carcinoma about 36 percent of the time.¹³ Individual studies have found rates that range widely. One study of 225 surgically excised papillomas without atypia reported an upgrade rate under 1 percent, while 93 atypical papillomas upgraded about 20 percent of the time.¹⁴ Another series found a 16 percent upgrade rate among 62 excised papillomas without atypia.¹⁵

The wide range reflects differences in how studies define atypia, how many tissue samples the biopsy needle collects, and whether imaging findings are concordant. Factors that raise the odds of an upgrade include larger papilloma size (over 1 cm), older age (over about 54), and discordance between the biopsy result and what the imaging suggested.¹⁶

Long-Term Breast Cancer Risk

Beyond the immediate question of hidden cancer at the time of biopsy, there is a separate question about future risk. One study followed 55 patients with benign papillomas after excluding those with other major risk factors and found that about 14 percent developed breast cancer over a median follow-up of roughly nine years. Interestingly, none of the patients who were managed without surgical excision developed cancer during that follow-up period.¹⁷ That finding is based on a small cohort, but it underscores that a papilloma diagnosis places a person into a somewhat elevated surveillance category, not unlike other proliferative breast lesions.

Treatment Options

For papillomas with atypia, the path is straightforward: surgical excision is recommended across essentially all guidelines, given the high upgrade rate. The real debate centers on what to do with benign papillomas that show no atypia on core needle biopsy.

Traditionally, surgical excision was the default for all papillomas. A study of 500 patients compared three management approaches for benign papillomas without atypia: surgical excision, ultrasound-guided vacuum-assisted removal (a less invasive procedure done under local anesthesia), and ultrasound follow-up without any intervention. The upgrade rate to malignancy was low across all three groups, about 1.9 percent after surgery, 2.1 percent after vacuum-assisted removal, and 0 percent with follow-up alone. Recurrence after vacuum-assisted removal was about 3.6 percent over two to five years of follow-up, and all recurrences turned out to be benign.¹⁸ Those results suggest that not every benign papilloma needs to go to the operating room.

A smaller series found that among patients managed conservatively (without excision), only one out of twelve later developed malignancy, leading the authors to suggest that observation may be a safe alternative for select patients.¹⁹ Current expert opinion generally recommends excision for papillomas with high-risk features (large size, imaging discordance, older patient age, multiple papillomas) while allowing imaging surveillance for small, concordant, clearly benign papillomas in lower-risk patients.⁸

Microdochectomy

When the primary complaint is persistent nipple discharge from a single duct, the standard surgical procedure is a microdochectomy, which removes the affected duct and whatever is growing inside it. A recent study of patients who underwent microdochectomy for nipple discharge found papillomas in about 58 percent of the surgical specimens, with ductal carcinoma in situ found in about 6 percent and invasive cancer in about 3 percent.²⁰ The procedure is generally well tolerated, though it can affect the ability to breastfeed from that duct.

Vacuum-Assisted Excision

Vacuum-assisted excision under ultrasound guidance has gained ground as a middle path between open surgery and watchful waiting. It uses a larger-bore needle with suction to remove the lesion in pieces through a small skin incision, typically under local anesthesia. Recovery is faster and cosmetic outcomes are better than with open surgery. In pediatric and adolescent patients, where the diagnosis is rare and preserving breast tissue is especially important, vacuum-assisted excision has been reported as a successful approach.²¹

Papillomas in Men

Breast papillomas are overwhelmingly a condition of women, but they can occur in men. The symptoms are similar: bloody or clear nipple discharge, sometimes with a palpable lump near the nipple-areolar complex. The rarity of male breast papillomas means they are easily misdiagnosed. One case report described an elderly man whose papilloma was initially mistaken for a sweat gland tumor on ultrasound, highlighting how imaging alone can mislead when the diagnosis is not expected.²² Because distinguishing a benign papilloma from a malignancy is not reliably possible through imaging in men either, surgical excision with histological confirmation is typically recommended.²³

Juvenile Papillomatosis

Juvenile papillomatosis is a distinct entity from a standard breast papilloma, though the name causes understandable confusion. It typically occurs in young women, often under 30, and presents as a localized breast mass without sharp borders. The tissue, when removed, has a characteristic “Swiss cheese” appearance due to large cysts mixed with areas of duct proliferation, sclerosing adenosis, and multiple small papillomas.²⁴ What makes juvenile papillomatosis clinically important is its association with family history: up to about 28 percent of affected patients have a family history of breast cancer.²⁵ A subset of patients with this condition go on to develop breast cancer themselves or have coexisting cancer at the time of diagnosis.²⁶ Because the clinical presentation resembles a precancerous lesion, it is frequently misdiagnosed before surgery, and the definitive diagnosis comes only from pathological examination of the excised tissue.

What Drives Papilloma Growth

At the molecular level, papillomas are relatively quiet tumors. Pure papillomas without atypia carry a low mutation burden, with a median of about one somatic mutation per lesion. The gene most commonly mutated is PIK3CA, which was altered in roughly 69 percent of pure papillomas in one sequencing study.²⁷ A separate study using highly sensitive digital PCR found AKT1 mutations in about 20 percent and PIK3CA mutations in about 28 percent of 60 papillomas. That study also showed something interesting about the origin of these tumors: when they separated the two main cell types within a papilloma (the luminal epithelial cells and the surrounding myoepithelial cells), both carried the identical mutation, suggesting that a papilloma grows from a single progenitor cell that can differentiate into both cell types.²⁸

PIK3CA and AKT1 are both part of a signaling pathway that promotes cell growth and survival, and mutations in these genes are also found in many breast cancers. That overlap raises the question of whether papillomas are an early step on a path toward malignancy. The evidence so far suggests that for most papillomas, the answer is no. The low overall mutation burden and the rarity of other cancer-associated gene changes in pure papillomas indicate that while they share a molecular starting point with some cancers, they usually lack the additional hits needed to become malignant. The genetic architecture of papillary lesions that do progress tends to show a higher complexity, with additional mutations accumulating in genes beyond PIK3CA.