It began with some skin spots on his back and a lump on his knee that he thought was just a bruise from a golfing injury. After a series of exams and a biopsy, David Tracy, 74, of Waterford, Conn., finally learned he had a very rare and puzzling blood cancer that didn’t even have a name until a decade ago.

BPDCN, which stands for blastic plasmacytoid dendritic cell neoplasm, “is a very interesting blood cancer that we didn’t know much about until 10 years ago,” says Andrew Lane, MD, PhD, a medical oncologist who directs Dana-Farber’s Blastic Plasmacytoid Dendritic Cell Neoplasm Center for research and treatment of the disease. Lane describes BPDCN as a “hybrid disease”: It affects the bone marrow and has some of the features of leukemia and lymphoma, and it also presents with characteristic skin tumors—sometimes a single spot, other times a rash, or even skin lesions all over the body.

Tracy, who was referred to Lane at Dana-Farber in the summer of 2018, is one of only a few hundred patients a year diagnosed with BPDCN in the United States. And what he found on the internet was scary: “I thought I only had about six months,” Tracy says.

BPDCN is very aggressive, and despite intensive treatment with chemotherapy aimed at achieving a remission so the patient can undergo a stem cell transplant, long-term survival has been limited. Most patients are older, and many aren’t candidates for transplantation.

Fortunately for Tracy, he was able to enroll in a clinical trial of which Lane is a principal investigator. The trial is testing an experimental drug that targets one of the malignant immune cells—which are identified by a marker called CD123—that are a hallmark of BPDCN. Known as tagraxofusp, the drug is a molecular guided missile carrying diphtheria toxin, which enters the CD123-marked cells and kills them.

In December 2018, tagraxofusp became the first drug ever approved by the U.S. Food and Drug Administration for treatment of BPDCN, making it a new standard of care for the disease.

“I have witnessed firsthand the significant responses a number of my patients experienced with tagraxofusp, and a proportion of responders were able to receive a stem cell transplant following remission,” says Lane.

The tagraxofusp clinical trial is continuing in an expansion phase. Meanwhile, Lane is heading two other clinical trials for BPDCN. One involves the Bcl-2 inhibitor venetoclax, and is based on work from Lane’s laboratory showing that the disease is particularly sensitive to drugs that block Bcl-2—a “survival protein” that allows some cancers to continue growing rather than obey molecular signals to self-destruct. The other is testing an antibody-drug conjugate that also binds to CD123 and delivers chemotherapy directly to the BPDCN cells.

One concern with tagraxofusp is that some patients develop a potentially dangerous side effect known as capillary leak syndrome, caused by the diphtheria toxin, which led to a boxed warning on the drug when it was approved. This risk is addressed by observing patients in the hospital during their first week of treatment.

David Tracy was an inpatient when he received his infusions of tagraxofusp last July and August and was fortunate in that he had few serious side effects. During his second cycle of treatment, he says he and his wife noticed the lesion on his knee flattening and becoming less prominent: “I felt that something really good was happening, and I was already feeling optimistic—hope began to appear.”

Following treatment with the new drug, Tracy underwent a course of conventional chemotherapy and total-body radiation to eliminate any remaining cancer cells. Then, over Christmas 2018, he received a stem cell transplant to restore his immune system. He says the initial lesions on his back and chest are mostly gone or fading.

“I’m OK,” he declares, “and I’m going to play golf this summer.”

This article was originally published on February 12, 2019, by Dana-Farber Cancer Institute. It is republished with permission.