Can this medicine cause lumps or cysts in the breast?

You did not write what drug it is. If you mean the drug Cyclo-Progynova tagged with the question, please read on. As for the other preparation, please add an additional answer with the correct trade name of the drug in this thread. Nodules or cysts in the breasts can be of different nature. In many cases, these are benign hyperplastic changes. Sometimes, however, the change in the breast may be cancerous. I have no information about what exactly change in your breasts you are asking. Medicines such as Cyclo-Progynova - like other drugs used in hormone replacement therapy - may increase the risk of developing breast cancer, depending on the duration of treatment. It is believed that the increased risk is evident after 3 years of using HRT. If you are taking Cyclo-Progynova, you should have your breasts examined regularly, and if any disturbing changes occur, you should consult your doctor. I enclose additional information about the preparation Cyclo-Progynova: https://www.gdziepolek.pl/produkty/20657/cyclo-progynova-tabletki-powlekane/apteki