PR or Progesterone Receptor, most commonly termed as NR3C3, is a type of hormone containing steroid inside the cells. PR of Progesterone receptors are usually available in the cancer affected cells in the breasts of the women. It is essential that detection of breast cancer should be tested for the presence of progesterone receptors. The testing should be done in a standard laboratory with proper procedure and specification. The presence of progesterone or PR in the breast cells may cause various hormones to malfunction and may also affect the growth and development of the breast in a normal manner.