part of mammary gland epithelial cell proliferation epithelial cell proliferation involved in mammary gland duct elongation dph 2009-06-22T10:58:12Z GO:0060750 biological_process The multiplication or reproduction of mammary gland branch epithelial cells, resulting in the elongation of the branch. The mammary gland branch differs from the bud in that it is not the initial curved portion of the outgrowth. branch elongation involved in mammary gland duct branching