Woman's 'extra breast' under her armpit developed a wart-like tumor in unusual case

In a rare case, painful swelling under a woman's arm turned out to be caused by a wart-like tumor growing from an extra breast in her armpit. 

The swelling had been growing for four years but had only recently become painful, leading the 63-year-old woman to seek medical attention. After examining the woman, doctors discovered that she had a spherical tumor growing within a milk duct of an extra breast under her left armpit. 

The tumor was not cancerous and was successfully removed with surgery, according to a report of her case, published July 22 in the journal Radiology Case Reports. 

This type of benign tumor is fairly common in normal breast tissue; it's found in up to 3% of breast biopsies. However, it rarely forms in extra breasts, so doctors may not always be so quick to diagnose and treat such unusual cases, the case report authors noted.

Related: Weird green bruise on woman's hand turns out to be rare tumor

While these tumors are rare, having extra breast tissue is more common than you might think.

Human breast tissue typically starts developing around the fourth week of pregnancy. At this point, cells that will eventually become the mammary glands, the tissue responsible for producing breast milk, start to form along a line that extends from the armpit to the groin on both sides of the body. These lines usually disappear a few weeks later, but in up to 6% of people, they persist, leading to the formation of an extra breast, also known as an accessory, supernumerary or ectopic breast. 

In the woman's case, doctors found that under her left armpit, she had a soft lump of tissue that was about 1.5 inches (3.8 centimeters) long and 1.5 inches wide. Over this lump, there was a patch of darker skin, which doctors initially suspected was an extra areola, the pigmented area around the nipple. An ultrasound of the tissue confirmed that the lump was indeed extra breast tissue, although the team determined that the darkened skin wasn't a true nipple. 

A magnetic resonance imaging (MRI) scan revealed that the lump contained a bleeding cyst. Doctors then extracted a tissue sample from the breast and discovered that the woman had what is known as an intracystic papilloma, a growth that develops inside a breast milk duct causing the walls to thicken and fluid to build up. 

Normally, these tumors are diagnosed and treated the same way whether they form in normal or extra breast tissue, the authors said. In this case, doctors removed the tumor and the woman went home the following day. 

Cases like these may raise awareness of the potential complications of extra breast tissue so that patients can be swiftly diagnosed and treated, the case report authors concluded.

"While examining a patient with axillary [armpit] swelling, accessory breast tissue conditions must be addressed as a differential diagnosis for early identification and therapy," they wrote.