There is no information in the provided sources regarding the effect of Lurbinectedin on breast milk production. The Drug Patent Watch [1] and MedlinePlus [3] do not mention anything about this topic, while the FDA label for Lurbinectedin [2] states that it is not known whether Lurbinectedin is excreted in human milk. Therefore, it is recommended that women who are breastfeeding should not breastfeed during treatment with Lurbinectedin and for at least one week after the last dose. Women who are considering breastfeeding should discuss the potential risks and benefits with their healthcare provider. It is important to always consult with a healthcare provider before taking any medication while breastfeeding to ensure the safety of both the mother and the infant.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/LURBINECTEDIN
[2] https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/213702s000lbl.pdf
[3] https://medlineplus.gov/druginfo/meds/a620049.html