This is the solution to the diagnostic mystery I posted Monday, in which a woman kept returning to the doctor with an apparent breast infection that wouldn't go away.
Dr. Lester and her colleague flipped through textbooks, searching for a solution to the puzzling case of the woman whose breast disease wouldn't go away. The patient had finally come to the surgeons and pathologist with a concern for an abscess, but Dr. Lester didn't find any signs of infection.
Instead, the pathologists found keratin, a protein made by a type of skin cell called a squamous cell, that gives skin its almost waterproof-like quality. Squamous cells and keratin are not found deep in the breast tissue, but Dr. Lester observed them lining the ducts that ordinarily carry milk. Why were there cells that looked like skin cells in the breast ducts?
The answer to this question is a grand mystery, one that goes further than the particulars of this case.
Nearly all cells in the body have an extraordinary capacity to regenerate and transform. Blood cells, for example, die every 120 days and are replaced by the bone marrow. The cells that line the gut wash away every few weeks and are replaced. We are, in a sense, regenerated every few years; even at age 60 or 70, our cells on average may be only 7 or 10 years old.
Such renewal seemingly promises endless youth, but the same forces that bestow cells with this transformative capacity are what give them the ability to become cancerous, growing recklessly and persistently, turning into tumors that look nothing like the tissue from which the cancer sprouted. Not all transformations are so dramatic. People who have chronic heartburn can slowly start to replace the skin-like squamous cells that line the lower part of the esophagus with the tall, intestine-like cells from the gut, in a process called Barrett's esophagus. Over time, this transformation may lead to esophageal cancer.
The woman in this story never had a true breast infection. Instead, something had coaxed the normal cells lining the milk ducts to transform into skin-like squamous cells. When this transformation was complete, the squamous cells behaved like true skin cells, rightly producing keratin - in the wrong location. The keratin accumulated abnormally in the patient's milk ducts, Dr. Lester explained, causing ducts to rupture, leading to inflammation and pain, and producing the patient's recurrent symptoms.
But what was it that compelled the cells in the woman's breast to transform into skin-like cells? No one knows for sure why this happens in the breast, but doctors have a pretty good guess. The process is similar to what happens to the airways of the lung in cigarette smokers. Over time, the cells that line the airways irritated by cigarette smoke start to stack on top of each other, turning into stronger, skin-like squamous cells. The changes are reversible - when the person stops smoking, the cells can revert back. But sometimes, they continue to change, increasing the risk for the development of lung cancer.
The transformative condition Dr. Lester and her colleague diagnosed in the breast is a rare observation called SMOLD, or squamous metaplasia of lactiferous ducts, where abnormal amounts of keratin accumulate in the milk ducts. In almost 90 percent of cases, patients with SMOLD are regular cigarette smokers.
Dr. Lester sees these cases rarely - in fact, many doctors have never encountered a case, but if not diagnosed, patients may go on to have endless recurrences, leading to ineffective treatments, long antibiotic courses, and anxiety.
But once SMOLD is correctly diagnosed, the treatment - removal of the affected milk duct - is curative. Quitting smoking might help too, but no one has studied this yet.
It's been many years since Dr. Lester was a pathology resident; she is now a recognized expert on breast disease, having written several textbooks and chapters in surgical pathology that trainees around the country use in their education. But despite her experience, she is still curious, passionate, and explores the human body with the same sense of mystery that the astronomer has towards the night sky. "What can you see with your eyes?" she asks herself every day, with papers, books, a microscope, students, physicians, and ultimately - patients, in mind.
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