The Uncanny eXpansion-Women

Fresh from another adventure battling Magneto in Genosha, the X-Men have returned home seeking out rest and relaxation.

However, while the ladies make their way down to the Mansion's spa for a girl's night out, a tired Kurt Wagner (the mutant better known as "Nightcrawler") decides he wants to spend his time off playing prank. Grabbing an unknown (but odd smelling) substance from Hank McCoy's lab, Kurt hides the substance in the ventilation shafts as the weekend's first practical joke.

But when the steam comes into contact with chemical fumes in the shafts, a surpsring chemical reaction occurs, causing all of the girls' breasts to grow to gigantic sizes.