Blastic plasmacytoid dendritic cell neoplasm (BPDCN)

BPDCN is a cancer of young plasmacytoid dendritic cells. These are rare immune cells that normally help the body sense viruses and raise the alarm. In BPDCN, immature forms of these cells grow out of control. It is a blood cancer, even when the first sign is on the skin. Researchers are still working out where these cells branch off in the marrow. They were long thought to come from the myeloid line, but some studies suggest they may also come from the lymphoid line.

The cancer cells often gather in the skin. They can also be found in the bone marrow, blood, lymph nodes and spleen, and in the brain and spinal cord. The disease has had several names over the years, so older papers may call it blastic NK-cell lymphoma.

Doctors diagnose BPDCN with a biopsy, most often of a skin spot, and often of the bone marrow too. Lab tests look for a pattern of markers on the cells, including one called CD123. BPDCN can look like other leukemias and lymphomas, so getting the diagnosis right matters: the treatment is different.

No one knows exactly what causes BPDCN. It is not caused by anything a person or their family did, and it cannot be caught from someone else.

In adults, the cancer cells often carry gene changes also seen in other myeloid blood cancers, such as changes in TET2 or ASXL1. These changes build up in blood-forming cells during a person’s life. Some people have BPDCN before, alongside or after a related marrow cancer, such as chronic myelomonocytic leukemia (CMML), myelodysplastic syndrome (MDS) or acute myeloid leukemia (AML).

Children with BPDCN tend to have different gene changes from adults. Researchers have not found an inherited risk, so BPDCN is not thought to run in families.

Most people first notice skin changes. These are often dark purple, bruise-like spots, raised patches or lumps. They often start on skin that gets sun, but they can appear anywhere on the body.

When BPDCN is in the bone marrow, it can crowd out healthy blood cells. That can cause tiredness, infections and easy bleeding. Swollen lymph nodes or a large spleen can also happen. Rarely, a person has no skin signs at all. Then the cancer is found because of low blood counts, swollen lymph nodes or feeling unwell.

BPDCN can reach the brain and spinal cord, often with no symptoms at first. So doctors check the spinal fluid with a lumbar puncture, or spinal tap, early in care. Even when the cancer seems to be only in the skin, it is treated as a whole-body cancer, because without treatment it spreads.

BPDCN is often first spotted by a skin doctor. After that, things can move fast: biopsies, scans, a spinal tap and a start to treatment, often in the hospital. A blood cancer team usually works with dermatology to follow the skin.

Treated skin spots can leave marks or color changes even when the cancer there is gone. Doctors may take a small biopsy to check. Waiting for these results can be hard.

If a transplant is planned, the months before it are about reaching remission and staying well enough. The transplant itself means conditioning, weeks in or near the hospital while the new cells engraft, and months of checks for infection and graft-versus-host disease. The team keeps watching for any sign that the cancer has returned.

A donor transplant for BPDCN uses healthy blood-forming cells from another person. The donor can be a brother or sister, another relative, an unrelated registry volunteer, or cord blood. In a registry study of 164 adults, about half of the donors were unrelated volunteers.

Timing matters. In that study, people did better when the transplant came during a first remission, and BPDCN that comes back is very hard to cure. When no family member is a good match, a registry volunteer can make a first-remission transplant possible.