Abstract
Background: Common sites of metastases from colorectal cancer include liver, peritoneum, and lungs. Brain and bone metastases occur infrequently. This report presents an unusual case of newly diagnosed Colon cancer with multiple brain and bone metastases with occult metastases to liver and lung only detected by using PET scan. Then we look over the possible hypothesis behind this enigma, trying to explain why our patient had brain and bone metastases in the absence of extra-cranial metastases on CT scan at the time of colon cancer diagnosis.
Case Report: A 59-year-old Caucasian female is presented with disorientation, headache and recurrent falls. She was recently diagnosed with Rheumatoid Arthritis and was started on Methotrexate. Brain imaging studies revealed multiple brain lesions. A CT scan of chest, abdomen and pelvis failed to show a primary origin. Blood tests detected iron deficiency anemia. And a colonoscopy found a colonic mass. Biopsies were positive for Adenocarcinoma.
PET scan demonstrated bone, lung, and hepatic metastases. Subsequently, patient underwent a transverse loop colostomy and partial omentectomy. She received whole brain radiotherapy, and she was scheduled to receive chemotherapy.
Conclusions: The systematic treatment of Rheumatoid arthritis with Methotrexate has partially suppressed the proliferation of extra-cranial and extra-ostial metastases to the extent they were not detected by CT imaging but only by PET scanning. And because Methotrexate could not cross the brain-blood barrier, the intracranial metastases manifested clinically before other metastases could cause any clinical symptoms or abnormal lab results.

Keywords: colon cancer, brain metastases, Iron deficiency anemia