Colorectal Cancer Metastases to Brain or Bone and the Relationship to Primary Tumor Location: a Population-Based Study.

BACKGROUND: The association of primary tumor location with incidence and prognosis of brain or bone metastasis in metastatic colorectal cancer (mCRC) patients remains unclear. We dissect this association across a large population. METHODS: A total of 202,401 CRC patients from the Surveillance, Epidemiology, and End Results (SEER) database between 2010 and 2015 were included. For brain metastasis, 9478 cases without brain metastasis information were excluded, leaving 192,923 CRC for incidence analysis and multivariable logistic/Cox regression analyses. Similarly, 193,013 CRC were eligible for bone metastasis analyses. RESULTS: The incidence of brain or bone metastasis at initial diagnosis was 1.38% and 6.12% in mCRC cohort, respectively. Median survival of CRC patients with brain or bone metastasis was 4 and 5 months, respectively. Primary tumor location is not associated with the incidence of brain metastasis but with bone metastasis. For bone metastasis, right-sided colon cancer (RCC) patients exhibited the lowest incidence, whereas rectal cancer (RC) patients had the highest. For both brain and bone metastases, RCC patients always had the shortest median survival, whereas RC patients had the longest. The common risk factors for brain or bone metastasis were grade III and multi-extracerebral or ectosteal metastases. The favorable prognostic factors for brain or bone metastasis were being female, married, insured, and RC. RCC is an unfavorable prognostic factor. CONCLUSIONS: Primary tumor location impacts incidence proportions of bone metastasis and survival of both brain and bone mCRC patients. Primary tumor location should be taken into consideration in clinical practice and prognostic assessment.