Metastatic Pattern of Breast Cancer by Histologic Grade: A SEER Population-based Study

Population-based estimates of the differences -in metastatic pattern, incidence, and prognosis of breast cancer patients by histologic grade at breast cancer diagnosis are lacking. Patients with breast cancer and metastases at the time of diagnosis were identified using the Surveillance, Epidemiology, and End Results (SEER) database. Multivariable logistic and Cox regression were performed to determine the effect of histologic grade on the presence of metastases at diagnosis and all-cause mortality. We identified a population-based sample of adult patients diagnosed with invasive breast cancer between 2010 and 2015 for whom the presence or absence of metastases was known. We depicted the landscape of metastatic pattern of breast cancer histologic grade that the percentage of bone metastasis was decreasing with higher histologic grade, while the percentages of lung and brain metastasis were increasing. Higher histologic grade was associated with a greater incidence of all metastatic lesions. Median durations of survival with distant metastasis were 41 months (Grade I), 34 months (Grade II), 21 months (Grade III), 13 months (Grade IV), and 16 months (unknown histologic grade). Grade III and unknown histologic grade represent the most common part of patients with metastatic disease, but not for breast cancer patients without metastasis. In multivariate analysis, Grade II, III, IV, and unknown histologic grade were associated with significantly greater odds of patients with metastatic disease to any distant site, compared with Grade I, but not to bone. Grade III was associated with increased all-cause mortality among patients having metastases to any sites, bone, brain, liver, and lung compared with Grade I, but not Grade II and Grade IV. Breast cancer histologic grades are associated with distinct patterns of metastatic spread and notable differences in survival.