Pharmacokinetics of methylene blue dye for lymphatic mapping in breast cancerimplications for use in pregnancy

Background: Although blue dye is routinely used for lymphatic mapping, it is not used for lymphatic mapping in pregnancy-associated breast cancer, because of concern of fetal risk. Methods: To investigate the safety of blue dye for lymphatic mapping in pregnant women, the pharmacokinetics of methylene blue dye were examined in 10 nonpregnant women, and the results were extrapolated to estimate maximal fetal exposure to the dye. Results: Plasma and urine measurements indicated that the dye quickly distributed from the breast injection site to the circulation, with 32% of the total dose excreted in urine within 48 hours. Combined with existing data on organ distribution of methylene blue, the estimated maximal dose to the fetus is 0.25 mg (5% of the administered dose), likely further reduced by other physiologic factors related to pregnancy. Conclusions: The analysis suggests that methylene blue dye can be used for lymphatic mapping in pregnancy-associated breast cancer with minimal fetal risk.