Multiple myeloma

Multiple myeloma is an out-of-control proliferation of plasma cells, the white blood cells that specialize in making antibodies. Normally there are a great many different plasma cells, each one making its own antibody against a different threat. Not here: a single plasma cell copies itself with nothing to stop it, and every copy makes exactly the same antibody. That is what clonal means, and the repeated antibody is called a monoclonal immunoglobulin.

This does not come out of nowhere. It is thought that first there is a silent phase called monoclonal gammopathy of undetermined significance: that repeated immunoglobulin can already be detected in the blood, but no organ is damaged yet and the person feels nothing.

When the disease advances, the usual pattern is for at least one of these to show up: the calcium in the blood rises, which is hypercalcemia; the kidney starts to fail; hemoglobin drops and anemia appears; or the bones hurt, with lytic lesions, which are holes in the bone. That last point has a concrete explanation: myeloma cells activate the osteoclast, the cell that breaks down bone, and at the same time they slow the osteoblast, the one that rebuilds it. More is destroyed than is built.