I found this piece from the American Journal of Medicine that discusses the case:
When Abigail Adams Smith, or “Nabby,” at age 46, noticed a lump in her breast, she decided to leave her family's farm in upstate New York and move back to her parents' home in Quincy, Massachusetts. She consulted with doctors Tufts and Rush, informing them her tumor was moving. Rush responded by mail to her father with this advice: “Her time of life calls for expedition in this business, for tumors such as hers tend much more rapidly to cancer after 45 than in more early life.” She must have a mastectomy.
Several Boston surgeons journeyed to Quincy, among them John Collins Warren, of Ether Dome fame. In November 1811, they performed a mastectomy on their patient in a bedroom of her parents' home. The operation lasted 25 minutes. They dressed her wound for an hour. Although suffering agonies, the patient displayed exceptional fortitude. But just 2 years later, an emaciated Abigail Adams Smith returned to Quincy to die, assisted only by opium. Abigail Adams wrote of her daughter's courage: “She told her physician that she was perfectly sensible of her situation and reconciled to it … Although she was bolstered up in her bed and could neither walk or stand, she was always calm.” McCollough writes that her father said “he had felt during Nabby's agony … as if he were living in the Book of Job.
From First Family by Joseph Ellis, here is more of Rush's advice to Adams on Nabby's situation:
From her account the remedy is the knife...I repeat again, let there be no delay in flying to the knife...It may be too late.