To better define the influence by host factors on very early breast cancer behavior, we retrospectively analyzed nodal status, diameter of the largest axillary metastasis (M), diameter of the primary tumor (P), the M/P ratio, tumor estrogen receptor status, age, obesity, and smoking habits in 176 women with node-positive breast cancer. Both M/P ratios and M were larger in the 72 obese women and in the 40 nonobese smokers than in the 64 nonobese nonsmokers after control for other factors. Step-wise regression analysis demonstrated independent associations between M/P ratios and obesity (p = 0.0002), larger primary tumors (p < 0.0001), more positive nodes (p < 0.0001), and smoking (p = 0.0268), as well as between M and obesity (p = 0.0201), larger primary tumors (p = 0.0093), and more positive nodes (p = 0.0001). Among the 104 nonobese women, smoking was associated both with larger M (p = 0.0257) and larger M/P (p = 0.0055). Our observations suggest more rapid growth by metastases in obese women and smokers with breast cancer, as well as earlier metastasis from their primary tumors.