I hope this is readable, my english is quite rusty since I don't have to write much.

Get a biopsie (if that didn't happen already, not sure from reading) with preferrably multiple samples. I don't know if you have that where you live, but where I live one sample is examined in the hospital and one to three samples are examined by external reference laboratories. The people in the hospital are good, but the people in the reference laboratories (my oncologist called them cancer nerds) are better since they often specialize on specific cancer groups and do noting else but examine cancer samples.

This way you get the best result, and if it turns out to be really cancer you can get the best treatment (definetly get a second opinion). If it turns out to be Lymphoma (non hodgkin to be precise, but hodgkin would be more likely) get your vitamin d levels checked if your doc doesn't check them on his own.

In case you get chemo newest studies show that vitamin d could be helpful [1]. Last year when I got my treatment the study was not finished but I asked my oncologist about it anyway. We checked and found out that I had only 4.4 µg/l of vitamin d3. It should be >30 µg/l, but if you live in northern areas it's likely to be between 20-30 µg/l if you're healty. Two years before my cancer was discovered I had my last vitamin d check and then it was >30 µg/l.

Also ask your oncologist about the rituximab level you will receive, newest studies show that young men and woman need a higher dosis than whats standard [2][3][4][5]

Speak to your doc about optimal 60. Some study results were presented at the international ash congress. It uses a liposomal formulation of vincristin and doubles the dosis. First results are realy promising and show even better results than 1.5 times the normal dosis.

Should you be a young high risk patient (young matches definetly) like me ask your doc about R-CHOEP 14. Studies show better results in young patients than the standard which in most countrys is R-CHOP 14 or 21.[6][7][8]

Depending on the chemo and other variables it could be that you should avoid some kinds of food. In that case remember the following sentence: "cook it, boil it, peel it or forget it".

Go for a walk/be active every day if you can, a good cardiovascular system distributes the drugs better and you preserve your muscles.

Avoid sick people and don't be near young kids if your chemo destroys leucocytes which is typical for Lymphoma treatment. In the earlier cycles your immunsystem should be able to handle it, but in later cycles sick people or young kids (they are ill often and depending on the chemo you can get sicknesses again that only kids get) are dangerous. My leucocytes dropped below 0.5 every chemo cylcle even though I had to take G-CSF to push my leucocytes. But discuss everything with your doctor.

Also, think about a port catheter. It has it's own risks but also benefits (it spares your veins) and makes the cancer treatment easier.

It's very likely that you are steril after chemo so bank sperm/eggs depending on your gender.

I'm the same age as you and was diagnosed with non-hodgkin lymphoma stage 4 (with multiple bulk tumors > 10cm and bone marrow involvement) last year after relly bad backpain for a few months. Which I thought came from my chair at work or my mattress since I was in good shape physically and my diet was balanced. But when I got checked for a herniated disk with an MRT they found the unwanted lodgers. After more checkups in the hospital they found them in my pelvis, spinal column, rib, muscles, spleen and lung but luckily not my brain or cerebrospinal fluid.

After getting 8 cycles of R-CHOEP 14 and 2 additional cycles with only Rituximab directly after that I am in complete remission. The PET-CT after my chemo showed that and now 3 months later my first aftercare CT shows that as well.

I wish you luck, and if it really turns out to be cancer, don't panic. Stay calm, think about your next steps (but I probably don't have to tell you that, since you showed that by asking here on ycombinator instead of putting your head in the sand like some people do) and do your research ,especially about newest studies, if you know your cancer type. My oncologist was very knowledgeable (lymphona is her speciality and she reasearches and publishes about it herself since 20 or so years) about newest studies but liked it that I informed myself and even found infos she did not read yet (no wonder, she gives around 500 chemos each year, teaches at university etc.). With this she could alter my chemo before my first treatment.

[1] Bittenbring J, Neumann F, Altmann B et al. Vitamin D deficiency impairs rituximab-mediated cellular cytotoxicity and outcome of DLBCL patients treated with, but not without rituximab . J Clin Oncol 2014

[2] Murawski N, Pfreundschuh M, Zeynalova S et al. Optimization of rituximab for the treatment of DLBCL (I): dose-dense rituximab in the DENSE-R-CHOP-14 trial of the DSHNHL. Ann Oncol 2014

[3] Pfreundschuh M, Poeschel V, Zeynalova S et al. Optimization of rituximab for the treatment of DLBCL (II): Extendet rituximab exposure time in the SMARTE-R-CHOP-14 trial of the DSHNHL. J Clin Oncol 2014

[4] Pfreundschuh M, Poeschel V, Zeynalova S et al. Increased rituximab doses eliminate increased risk of elderly male patients with aggressive CD20+ B-cell lymphomas: Results from the SEXIE-R-CHOP-14 trial of the DSHNHL. J Clin Oncol 32[6], 2014

[5] Pfreundschuh M, Schubert J, Ziepert M et al. Six versus eight cycles of bi-weekly CHOP-14 with or without rituximab in elderly patients with aggressive CD20+ B-cell lymphomas: a randomised controlled trial (RICOVER-60). Lancet Oncol 2008;9:105-16.

[6] http://www.ncbi.nlm.nih.gov/pubmed/21460380
[7] http://www.ncbi.nlm.nih.gov/pubmed/23168367
[8] http://i.imgur.com/bq5ZZsr.png