When Tianna Moon was diagnosed with a rare condition that causes runaway breast growth, she did not retreat from the stares and the pain. Instead, the 30-year-old from East Anglia turned her medical reality into a lucrative career. On the subscription platform OnlyFans, where she began posting after a head injury in 2021 left her unable to work, she now earns around £10,000 a month from admirers of her fuller bust. “I might as well try and reap the benefits of my medical condition rather than the negatives,” she says.
Tianna, who measures in at a 32OO cup size, claims her breasts are “Britain’s biggest” and entirely natural. Unlike others who may claim the title through cosmetic enhancement or by relying on US bra sizing, she says, “My situation is different as my chest growth is entirely natural. I just let my boobs do what they want.” The online attention is not always positive — she has been told her condition is “disgusting” and accused of “begging for attention”. Her social media accounts have even been temporarily banned because some users speculated her natural breasts were AI-generated. But she dismisses the criticism: “When I was younger I hated the attention but now I just think they could be a potential buyer, and my subscribers aren’t creepy, they genuinely love my breasts and support me.”
Turning a Rare Condition into a Career
Her OnlyFans career began almost accidentally. After a head injury prevented her from working full-time, she joined the site in 2021. As her breasts grew, subscribers themselves urged her to get remeasured. “That’s when I started monitoring them,” she recalls. Today, her income reflects the growing interest, and she sees her body as an asset rather than a burden. “I might as well try and reap the benefits,” she insists.
The Diagnosis and Daily Toll of Gigantomastia
It was only last year that Tianna learned why her breasts were so unusually large. She was diagnosed with gigantomastia, a severe form of macromastia — a condition that causes rapid and excessive growth of breast tissue. Fewer than 300 cases have been recorded worldwide, making it extremely rare. The key trigger for her diagnosis came when she began taking the weight-loss drug Mounjaro in May 2024. Over the following year, she lost three stone (approximately 19kg), yet her breasts grew from an L cup to an M cup, and eventually to her current 32OO size. Noticing the oddity — that her body was slimming while her chest was expanding — she searched medical discussion groups online and “stumbled across” gigantomastia. A visit to her GP in July 2025 confirmed it. “Originally he was looking at macromastia but when I broke down medical history, the weight loss on Mounjaro and the increased growth and side effects, he was point blank like ‘this is gigantomastia’,” she says.
The physical toll is severe. Her breasts are estimated to weigh about 39 lbs (around 17.7kg), roughly 20% of her total body weight. This causes constant pressure on her body. “The side effects are having numb arms quite a lot and having quite severe indentations on my shoulders,” she explains. “Things like running and jumping can be risky, since they often smack me in the face.” She has light scarring under her breasts where bras have rubbed and ripped the skin open. Lying on her back for long periods is impossible because it restricts her airflow. “Also laying on my back is not something I can do for a long period of time as it restricts the amount of air flow I can get in,” she says.
Finding a bra that fits has proved nearly impossible. Standard UK manufacturers stop at an M cup, and wearing the wrong size causes pain. “Even before I maxed out the sizes, my breasts would often break the wires clean in half,” she says. She tried buying the largest available sizes and making them work, but that led to cuts and infections under her ribs. She has recently given up on bras altogether and says she is happier without them.
Tianna is not alone in facing these challenges. Summer Robert, 25, from Scotland, also lives with gigantomastia. She measures around a 30N or 28 O-cup, depending on the shop, and carries approximately 25kg (around 55 lbs) of breast weight daily. She has been refused breast reduction surgery multiple times due to her BMI, despite much of her weight being attributed to her chest. To cope, she wears a doctor-prescribed corset. “I’ve worn one since I was 16 because if I’m walking my back feels like it’s broken – it’s so intense and painful,” she says. “I swim a lot because I’m weightless so it’s a relief, but then I get out the pool and it feels horrific.” Like Tianna, she has turned to OnlyFans, building a loyal following that supports her and helps her feel confident.
Bra sizing in the UK is notoriously inconsistent. Sizing systems vary between countries and manufacturers, leading many women to wear bras that are two sizes too small. The concept of “sister sizes” — brackets with the same cup volume but different band sizes — does not apply to the extreme cup sizes faced by women with gigantomastia. Breast reduction surgery in the UK can cost between £6,500 and over £10,000 privately, while NHS eligibility typically requires significant health problems and a BMI below 26, with a minimum expected volume reduction of 500g per breast.
Mounjaro, the weight-loss drug Tianna took, is primarily used for blood sugar regulation and weight loss. Direct side effects targeting breast tissue are not established; breast changes during weight loss are usually attributed to overall fat loss. However, Tianna’s case — where breast tissue continued to grow disproportionately despite significant weight loss — is unusual and prompted her search for answers. The condition gigantomastia differs from macromastia in its rapid and extreme nature. (It is also distinct from gynecomastia, a condition of enlarged breast tissue in men.)
What Lies Ahead: Treatment and Uncertainty
Looking to the future, Tianna has taken steps to manage the physical burden. In November 2025, she underwent private gastric sleeve surgery — a procedure that reduces the stomach’s capacity to aid weight loss — specifically to “protect her back” and prevent further pain. She has also been referred for physiotherapy to help manage the pain associated with her condition. Initial physiotherapy appointments in the UK can start from around £100, though total costs vary.
Breast reduction surgery remains a possibility, but Tianna is cautious. She has looked into it but says there is “no guarantee” her breast tissue will not grow back. In the UK, NHS eligibility for breast reduction is strict, often requiring a BMI below 26 and a minimum expected tissue removal of 500g per breast. Given the rarity of gigantomastia, even private surgery carries uncertainty. “Although I do hope they stop at some point,” she says.