[catkeson]

Kappa free light chain level down, M-spike still high

by catkeson on Fri Mar 16, 2018 1:57 pm

Hello,

A family member has recently gone through induction therapy with Revlimid, Velcade, and dexamethasone (RVD) in preparation for an autologous stem cell transplant. He has come a long way since diagnosis, with his kappa level down from about 1000 mg/L to 40 mg/L, and his M-spike down from 7 g/dl to 0.8 g/dl after 4 cycles.

The surprising thing is that in his fourth cycle, his kappa dropped almost 80%, while in the first three cycles it was just dropping at about a 30% rate.

Anyway, we are going to do one more cycle to try to lower his M-spike and get the kappa to the normal range.

What I am confused about is the discrepancy between his kappa levels and M-spike. I thought they were basically tied to each other since they both measure disease burden. I don't understand how his kappa levels could be so close to normal, but his M-spike still has a ways to go.

Is there a lag in the M-spike? Are M-spike and kappa measuring proteins that are produced by different kinds of cancer cells?

Any information would be greatly appreciated.

[Multibilly]

Re: Kappa free light chain level down, M-spike still high

by Multibilly on Fri Mar 16, 2018 8:00 pm

Hi Catkeson,

Monoclonal free light chains and monoclonal immunoglobulin levels (m-spikes) don't necessarily track during disease progression and / or during treatment. Also, the half lives (the amount of time it takes for 50% of a particular molecule to degrade in the body) are quite different for free light chains and immunoglobulins. The half life of a free light chain molecule is about 6 hours. On the other hand, the half life of an IgG molecule is about 21 days. So, you would naturally expect one's free light chain levels to respond more quickly to treatment than you would one's m-spike level.