Boobpedia - Encyclopedia of big boobs
Isabelle Lanthier is a French Canadian woman with gigantomastia.
She appeared on Montel Williams' talk show, where she told how her chest grew from 34 inches (86 cm) to 52.5 inches (133 cm) in five months during her pregnancy (Her breast growth was incipient to pregnancy).
This is an increase of over 18 cup sizes making her at least an R cup and, at their largest, one breast weighed 15 pounds (6.8 kg) and the other 12 pounds (5.4 kg).
Her husband custom made a special bra to support her breasts.