Fig. 4

a Radial Basis Function Network (RBF) demonstrates that subcategories of BC and age at primary diagnosis are the most important independent variables for development of bone-only metastasis. The normalized importance of subcategories of BC is 100 % and of age at primary diagnosis 45 %. Independent Variables: age at primary diagnosis, tumor size, nodal status, grading, subcategories of BC, histological subtypes, Nottingham prognostic index. Dependent Variable: bone-only metastasis. b Multilayer Perceptron (MP) also demonstrates that subcategories of BC and age at primary diagnosis are the most important independent variables for development of bone-only metastasis. The normalized importance of subcategories of BC is 100 % and of age at primary diagnosis 62.9 %. Independent Variables: age at primary diagnosis, tumor size, nodal status, grading, subcategories of BC, histological subtypes, Nottingham prognostic index. Dependent Variable: bone-only metastasis