Die Brust.

A peculiar short novel by a favorite author of mine who you've probably heard of recently because he's the writer of [b:The Plot Against America|703|The Plot Against America|Philip Roth|https://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1553896240l/703.SY75.jpg|911456], which is now (March, 2020) an HBO series. As the description of it says on this site, [a:Philip Roth|463|Philip Roth|https://images.gr-assets.com/authors/1399886959p2/463.jpg]is, in [b:The Breast|50990|The Breast|Philip Roth|https://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1327936311l/50990.SY75.jpg|387473], entering into [a:Franz Kafka|5223|Franz Kafka|https://images.gr-assets.com/authors/1569196898p2/5223.jpg]'s [b:The Metamorphosis|485894|The Metamorphosis|Franz Kafka|https://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1359061917l/485894.SY75.jpg|2373750] territory. (An aside. Want to know something about The Metamorphosis most don't? Nowhere in the original does it say the guy woke up as a cockroach. He's called "a hideous vermin," but it's never given a name.)
The book is a heady thing, a musing on transformation and madness. It's very much of its time, which is 1970 or so (it was published in 1971).
At one point, the narrator doubts he has actually turned into a 155-pound breast and has gone mad instead:

How explain the "mammary envy" that might be thought to have inspired so extravagant an invention? Was I just another American boy raised on a diet too rich with centerfolds? Or was it rather a longing in me, deep down in my molten center, a churning longing to be utterly and blessedly helpless, to be a big brainless bad of tissue, desirable, dumb, passive, immobile, acted upon instead of acting, hanging, there, as a breast hangs and is there. Or think of it as a form of hibernation, a long winter's sleep buried in the mountains of the female anatomy. Or, or, think of the breast as my cocoon, first cousin to that sac in which I had tread my mother's waters.