A 30-year-old woman in the United Kingdom, Tianna Moon, was diagnosed with a rare medical condition called gigantomastia after her breast size continued to grow even as she lost significant body weight with the help of the prescription weight-loss drug Mounjaro (tirzepatide). The case has drawn attention because it contrasts the expected pattern of fat loss during medication-assisted weight reduction.
Mounjaro is a GLP-1 (glucagon-like peptide-1) receptor agonist originally developed for managing type 2 diabetes. It also has an approved indication for chronic weight management in adults with obesity or overweight when used with lifestyle changes. These medications work by slowing digestion and reducing appetite, leading to reduced food intake and weight loss.
In Tianna’s case, she reportedly lost five stone (about 70 pounds) with the help of Mounjaro but began to notice that her breasts were increasing in size rather than decreasing proportionally with her overall body weight loss. She described finding her chest size had grown to an estimated 34NN cup size, a measurement reflecting extremely large breasts.
Tianna was subsequently diagnosed with gigantomastia, a rare disorder characterized by excessive and rapid breast tissue growth. Unlike common variations in breast size, gigantomastia involves disproportionate enlargement of breast tissue, which can pose physical and functional challenges such as:
Musculoskeletal strain, including back and shoulder pain
Skin irritation and breakdown beneath the breasts
Posture changes and mobility limitations
Difficulty finding supportive clothing or bras
Medical literature notes that underlying causes of gigantomastia can include hormonal changes, immune-mediated disorders, medications, and genetic factors. Although the exact trigger in Tianna’s case is unclear, the condition was identified after her medication-assisted weight loss, prompting a healthcare evaluation.
According to reports, Tianna has experienced a range of physical symptoms due to breast size, such as:
Numbness in the arms
Shoulder indentations from bra straps
Back pain
Difficulty breathing when lying flat
Skin irritation and scarring
Challenges finding suitable clothing and supportive undergarments
These effects reflect the functional burden of extreme breast enlargement, which can impact everyday activities and comfort. Because gigantomastia causes continued breast enlargement, some patients consider breast reduction surgery, although outcomes vary and there is no guarantee that tissue growth will not recur.
Gigantomastia is rare, with fewer than 300 reported cases globally. This condition differs from macromastia, a less severe and more common form of large breast tissue enlargement. Clinical descriptions note that gigantomastia may be associated with significant hormonal changes or underlying immune disorders, though exact mechanisms are often unclear. Its rarity means that evidence on causation and management is limited, and each case may present uniquely.
GLP-1 receptor agonists, including Mounjaro, are widely used for weight management and type 2 diabetes because of their effectiveness in reducing body weight and improving metabolic control. However, they also have documented side effects, primarily gastrointestinal issues such as nausea, vomiting, and diarrhoea, and serious but rare complications like pancreatitis and gallbladder disease. These medications should be prescribed and monitored by healthcare professionals as part of a comprehensive treatment plan that includes diet and exercise.
Reports of breast size changes among individuals losing weight are not a well-established medical effect of these drugs; most anecdotal accounts relate to typical fat loss patterns in response to reduced adipose tissue. Tianna’s diagnosis of gigantomastia remains an uncommon medical finding in the context of a weight-loss journey assisted by Mounjaro.
(Rh)
