Hi, When somebody has an abrupt shooting pain in buttocks after cough or sneeze, this means that something is irritating a nerve when abdominal pressure increases. The most common cause could be a discopathy at lower lumbar or lumbosacral area (that means at least one of the intervertebral disks is protruded). But as you mentioned a strong family history of cancer you should take more careful steps. My advice as a professional is to take a lulmbosacral and pelvic MRI study. You should ask an expert radiologist to report the MRIs to rule out any other space occupying lesion which can irritate the nerves and also evaluate the lymph nodes you mentioned. According to the result of the MRIs, the next steps should be revealed. Until you get the MRIs, you can do some precautions to decrease the problem. For example you should have your knees slightly bent when lying down (avoid full extension of the knees to reduce potential pressure on nerve roots). Also, if this problem really bothers you, you can use an anti-inflammatory medication such as Ibuprogen, Naproxen or Diclofenac for a few days. Again, I advice to take the lumbosacral and pelvic MRI study whenever you can. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Hooman Mahmoudi, Neurologist