PGR and cancer: However, SD cancers are not only smaller than clinically presenting cancers but also more indolent biologically as they are lower histological grade, express p53 and Ki-67 nuclear proteins less frequently, and have fewer mitotic cells, more moderate/rich oestrogen and progesterone receptor levels, and lower levels of microvessel density (Uyterlinde et al, 1991; Hakama et al, 1995; Moezzi et al, 1996; Tabar et al, 1999; Groenendijk et al, 2000; Ernst et al, 2002).