Paul, My understanding is the re-occurrence is the same type B cell. The b cells, good and bad, are made in the bone marrow and after treatment, the bone marrow continues to produce more good and bad b cells. My really basic understanding is that for some unknown reason my bone marrow started to produce these smaller than normal bad b cells, A normal b cell has a life span of a couple weeks and they die off and are filtered out by the spleen. The bad b cells don't act like a normal b cell in fighting infections, etc and they don't die. And since they don't die or have a much longer life, they go to the spleen and accumulate and my spleen grew and grew over a number of years. Rituxan kills all the b cells and the spleen sort of goes back to normal size. The bone marrow is still making bad b cells and the spleen will gradually get larger again. Each person is different and some seem to have better treatment results. Some SMZL will morph into something else as well. Clarify all this with your doctor.
The start of my SMZL journey was a high white blood count and low platelet count during a routine physical in 2019. Doctor looked back in test results and figured it started prior to 2017 as levels were changing back then. My primary care doctor referred me to a local oncology group and could not get in for a month. I called Mayo and got in within a week and was diagnosed the following week. I did keep my original oncology appointment and they confirmed the Mayo diagnosis and I kept going to Mayo. At Mayo, the Hematology group works with the blood cancers and within that group, there are a some that see the marginal zone/B cell lymphoma patients. I get blood tests and appointment there every 6 months.
A Mayo second opinion would involve getting copies of or releasing all of your medical records so Mayo could see all imaging and test results.
My 2019 testing also found a really early stage lung cancer and have had two lung surgeries since then. I also see an Oncologist every 6 months, too.
So I have had a lot of care in Rochester and am very very pleased with everything they have done.
I know, this was hard to learn and live with. Gradually it became my new normal.
Hope this helps you.