Well, I had something called CUP (Cancer of Unknown Primary), but it had similarities to squamous cell and small cell cancer. I was treated with taxol/carboplatin, and then 5 weeks of radiation therapy. Carboplatin/taxol are both used for squamous cell cancer.
The taxol/carbo chemo was a bit weird. Because my oncologist is wonderfully proactive about preventing nausea, I had absolutely no nausea and no loss of appetite. In fact, I gained two pounds during chemo! (Then I went on a cruise and lost two pounds...my doctor has determined that my medical diagnosis is "weird syndrome", lol). At any rate, the taxol did cause excruciating pain, but not on the day it was administered; rather, the pain would start about 36 hours afterwards and last for about 3 days. I would spend those three days doped up on Vicodin, and then be okay for the next three weeks (until the next treatment). Now, I have fibromyalgia, so I'm pretty much in constant pain anyway...people without FM usually don't have quite so bad a response.
At any rate, I have been totally cancer-free for 3 1/2 years...and CUP usually has a terrible prognosis.
So, my ultimate advice? OPTIMISM!!! Don't count your Dad out yet! This may very well be curable, or if not curable, manageable. By that I mean that he may have to have some treatment periodically, but could still live a happy and productive life for many years.
Keep me posted, Kim, and have your Dad post himself if he'd like to "chat" about his situation.