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The contracted gall bladder was also mentioned in your CT scan report. But that does not lead to an enlarged spleen. Apart from malignancy many other non-neoplastic conditions as well can lead to spleen enlargement like chronic infections, malaria, autoimmune disease like lupus, hemolytic anemia. If no specific cause is found, then it can be considered idiopathic without any reason. But HB estimation, peripheral smear examination report, ANA, etc., like investigations, can be done as per requirement.
Your lactic acid level is within the limit and so do not worry about that. The elevated CA 27.29 points towards breast cancer but it is not the rule. Its elevation cannot be solely considered as the diagnosis of some form of cancer. If you have cancer then CT scan would show any growth or mass. But CT scan report is normal.
Your doctor will do your breast examination to rule out any mass or lump if present. The bilateral flank pain points towards some kidney disease. For that, I already mentioned investigating with urine routine microscopic examination and culture report. Serum urea, creatinine estimation also should be done. If they all are within limit then gastritis and diverticulosis can be the reason.