G1K-immunoglobulin recombinant monoclonal antibody is indicated in certain cases of melanoma. Its high molecular weight explains the observed very low-excretion into breastmilk (Ross 2014). Its low oral bioavailability hinders the passage from ingested milk towards the infant’s plasma, except in preterm babies and immediate neonatal period, which may show an increased intestinal permeability. Although possibly safe during lactation, a long elimination half-life span (14.7 days) and its serious side effects (Beck 2006, Araujo 2015) make it necessary not to breastfeed until more data on this drug are available.The period for “washout" (obligatory time period for the drug to be completely eliminated from the body) that should be observed before resuming breastfeeding would be 74 days (5 times half-life period) after the last dose.A woman who nursed her infant after 21 days from the last dose (Ross 2014) did not report side effects in the infant.