A composition and associated method for chemical mechanical planarization (or other polishing) are described. The composition comprises an organometallic-modified colloidal abrasive and a nitrogen-containing polymer compound (e.g., a polyalkyleneimine, such as polyamidopolyethyleneimine). The composition possesses both high stability towards gelling and/or solids formation and high selectivity for metal removal in metal CMP. The composition may further comprise an oxidizing agent in which case the composition is particularly useful in conjunction with the associated method for metal CMP applications (e.g., copper CMP).