At left are crops of two panels from a recent Breast Expansion Story Archive comic called "Stranger than Fiction". In the story, a young man finds that all of the women in his life are being transformed into incredibly stacked and curvy sex goddesses. He knows that he is the cause of it, but can't seem to control his ability to transform.
In the panels at right, his best friend's kid sister goes from being a teen squirt to chesty babe, and then very chesty (the leftmost of the two panels) and finally an insanely chesty twenty-something uber-babe.
I've had worse times than reading this story. Flat-chested to 'bigger than her head' is my favorite breast growth story. And in this one, all the women wind up gigantically big-titted, no matter how small they start.
Click on the image above left.