It was a blow that you have to go such an ordeal. It must have been a stressful situation and life changing experience.
To begin with, lipoma is a benign lump, which is non-cancerous. It grows from the fat cells that are present in the body. The lipoma can be left untreated if it is not causing discomfort, but if pain is noted, it will be surgically removed and will be sent for biopsy. On the other hand, enlarged lymph nodes are part of our body's immunity and these are swollen when infection is evident. Now, in your case, the enlarged lymph nodes turned out to be SLL. The lymphoma is considered indolent. This means that the disease progresses VERY SLOWLY, and patients are diagnosed lately because of its slow development.
As for negligence and malpractice,try to visit this site, to know when you can file a claim or not about the misdiagnosis: Medical Mistakes -- A Primer on the Basics of Medical Malpractice
. It was a short article from Mr. Haskell, a popular lawyer in Spokane WA that has won a bunch of million dollar legal claims. That will supplement you with information about medical issues, and further widen your horizons about medical malpractice.