How is multiple myeloma classified by type?

What are the different types of multiple myeloma? How is myeloma classified? 

Classification system for multiple myeloma has to do with what kinds of proteins the myeloma cells make. Myeloma is a cancer of plasma cells, and plasma cells are usually the normal cells in our body that produce antibody proteins to help fight off infections. That means that myeloma cells, because they are plasma cells, also usually make an antibody. And because the myeloma cells are all copies of each other, that's what makes them cancer cells. They all produce the same useless antibody protein for most patients with myeloma. For most patients with myeloma, their myeloma cells do indeed produce an abnormal antibody or a fragment of an antibody that's called secretory myeloma. For most patients with secretory myeloma, the antibody that their plasma cells produce is a full or intact antibody, which is made up of two protein chains attached to each other: a longer or heavy chain attached to a shorter or light chain. We name heavy chains conventionally using regular letters G, A, M, D, or E. The light chains have the Greek letters kappa or lambda, and so most people with myeloma will have a full antibody associated with their myeloma, which we might call an IgG kappa antibody, or an IgA lambda antibody. More rarely, an IgM kappa or lambda antibody. Some patients, even those whose myeloma makes a regular antibody, also have cells that just make that light chain fragment of the antibody, so that only make the kappa or lambda light chains. While everybody, healthy people included, have low levels of kappa and lambda light chains detectable in their blood, in someone who has myeloma making an abnormal light chain, one of those numbers will be much higher than the other. So, for instance, someone with an IgG kappa multiple myeloma might also have an elevated level of free kappa light chains. For a subset of patients with secretory myeloma, what it mainly affects is how we primarily measure the myeloma. For someone whose myeloma makes a full antibody, we usually think of the primary measurement of the myeloma being the level of the full antibody. The level of the full antibody is usually measured in a test called serum protein electrophoresis or SPEP, which measures the M-spike, also known as the M protein, myeloma protein, or monoclonal protein. We sometimes also measure that full antibody using the total IgG or IgA level as a perhaps more accurate measurement than using the serum protein electrophoresis. For somebody whose myeloma is only measured using light chains, we primarily measure that in the blood using the serum free light chain analysis and look at the levels of kappa or lambda light chains, and to a lesser extent, at the ratio of kappa to lambda light chains, because that number can change a lot just based on the lower number of the two. It's probably the absolute number for the kappa lambda light chain that's the most important. For many patients, especially those whose myeloma makes light chains, you can also detect those light chains in the urine using a test called urine protein electrophoresis or UPEP. That often requires doing a 24-hour urine collection, although sometimes we can get useful information from a small urine sample. It's only a very small subset of patients with myeloma, probably around 2 or 3%, whose myeloma cells do not make any of those abnormal proteins. Those patients have what we call non-secretory myeloma. Non-secretory myeloma can be more challenging to treat primarily because the proteins that we usually measure in the blood as our key indicator of whether the myeloma is shrinking or growing aren't available to us. We're stuck using other measurements of the myeloma, either looking at how many plasma cells there are in the bone marrow over repeat bone marrow biopsies, or looking at how much myeloma we can detect in lumps throughout the body on imaging studies like a PET scan or a CT scan, or a combined PET CT scan. But the overall treatment of non-secretory myeloma is pretty much the same as for secretory myeloma, the main difference being in how we're following the disease.