My patient, a yoga instructor, had already received a week of chemotherapy, so he couldn’t be called a complete newcomer to the side effects of his treatment. But he was still bracing himself for what was yet to come.

He was in his 70s and had a rare variety of a rare cancer: acute lymphocytic leukemia, which affects fewer than 3,000 adults yearly in the United States, along with the more common acute myeloid leukemia. Usually, leukemia chooses to corrupt only one tribe of our white blood cells: myeloid or lymphoid, the soldiers of the immune system; his had chosen both.

In response, we decided on therapy that would try to clobber both leukemias at the same time.

The drugs had hit the mark, as the leukemia had disappeared entirely from his blood stream. But they had also missed, taking a whack at his liver and disrupting how his body processed the bile the liver usually makes to help digest food. This misfire had transformed his skin and the whites of his eyes to a painful-to-view fluorescent yellow.

The drugs had also inflamed and eroded the tissue lining the inside of his mouth and esophagus. The pain that resulted made it nearly impossible for him to consume even the thinnest of liquids. One patient told me that with this condition, called mucositis, drinking water was like trying to swallow glass.