PGR and cancer: Furthermore, Fig. 4 presents the results of the differential lipidomics analysis of saturated and monounsaturated phosphatidylcholine (PC) between ER (+) (Estrogen Receptor-Positive, indicating high levels of estrogen in the cancer cells) and ER (−) samples, as well as PR (+) (Progesterone Receptor Positive, indicating high levels of progesterone in the cancer cells) and PR (−) samples, under conditions where HER2 is negative.