Filgrastim is a Granulocyte-Colony Stimulating factor (G-CSF). It is an FDA approved drug. Very small embryonic-like stem cells (VSELs) are found in the ovary. Animal studies showed that these cells are able to regenerate the affected ovary. Studies on mice have shown that Filgrastim result in recovery of oogenesis after chemotherapy-induced gonadal failure (in 2013, 2014, and 2015).