More answers might start to roll in after dark.

I'm not a doctor, so I'm hesitant to recommend anything, and only offer my own experience, which (short version) was: Diagnosed at stage 2 w/ tumor in pancreatic head; 6 months of chemo (FOLFIRINOX); successful Whipple (with maybe one big exception); 4 months with no real evidence of disease; discovery of tumor recurrence at the Whipple site 4.5 months post-op; confirmation 6 weeks later it had spread; now on new chemo (Gemcitabine+Abraxane+Cisplatin).

I had been experiencing back pain after the first diagnosis, but was lucky enough to discover it was only tight muscles a physical therapist was able to work out.

My first symptoms in order were: Abnormal liver enzymes, weight loss, stool & urine changes, the mild jaundice (eyes), then more jaundice (eyes & skin discoloration), then the itching from a blocked bile duct.

It was about 3 months from abnormal liver enzymes to a definite diagnosis. My doctor started down the "obvious" path of assuming a liver issue based on the bloodwork.

Diagnosis steps included ultrasound of liver (inconclusive) repeat blood tests (mostly checking for hepatitis, and liver enzymes, which went up and down before finally going on an upward tear.) That finally led to an MRI -- I think the generic abdominal MRI rather than the MRCP method focused on pancreatic issues. It did identify a growth on the pancreas, but was not very specific.

Next step was an EUS (Endoscopic UltraSound) and ERCP with a biopsy, which confirmed malignant cancer cells, deemed "resectable." PET scan confirmed one tumor and no metastases, which led to the treatment described above. (They also inserted a stent to open my bile duct when they did the EUS.)

What I later figured out is that we could have done an early blood test for CA19-9 for $25 to get a first check for pancreas issues (including pancreatitis).. It's not the gold standard or a final diagnosis, but one piece of many that may confirm each other. There are other cancer markers like CEA, CA-125, etc that can also be ordered by a primary care doc to check cheaply and quickly.

You should definitely ask a doc to order you a germline genetic test like Invitae to see if you inherited mutations that make you more susceptible to certain cancers. That may help zero in the diagnosis now and guide treatment later, if necessary.

You can also contact Grail about their "Galleri" multi-cancer panel. You can chat with one of their medical reps over the phone to get the simple blood test approved. It's about $950 and you'll have to self-pay, but it MIGHT help identify a cancer. There are no guarantees it works either way (not FDA approved; can give a false positive or false negative), but it can be another piece of the puzzle to support or contradict the others. In my case, it failed to report any cancer when MRI a few weeks later found my "new" 2 cm tumor on my pancreas.

There's another test ("360" from Guardant) that can also detect tumor DNA in your blood, along with any mutations it has, which would help guide your treatment. These are all easy enough to do with simple blood tests, and SHOULD be do-able without delay.

In my recurrence, it was kind of the opposite experience of yours. Once the MRI spotted my tumor had come back (and agreed with the rising CA19-9 levels, in spite of two "fancy" DNA tests not detecting it), another EUS was done to get a biopsy, and even that came back negative, so everyone was really confused.

So... there are lots of puzzle pieces to put together. I can't tell which blood tests you've had (traditional biomarkers and newer DNA-based tests), but those are something you should pursue if you haven't already.

There are lots of surprises in this world, and sometimes two things that seem inextricably linked have nothing to do with each other. With your back pain, you might have to consult a neurologist to see if spinal or nerve damage is causing it. There could be spinal stenosis pinching a nerve, a tumor pinching a nerve, or many other causes. I've heard (not confirmed) that esophageal cancers can metastasize to the spine.

All the above is speculation, but I'll say don't take NO for an answer -- it sounds like you've got something very real going on, and you mustn't stop until they identify it. Best wishes to you.