Patient cream assignment will be un-blinded at the 8 or 9 week time period (depending on the chemotherapy). However, patients with a 2 grade improvement in PPE in one hand versus the other (e.g. grade 3 improves to grade 1, or grade 2 improves to grade 0) that is maintained for at least 2 weeks, will be eligible for early un-blinding and treatment with active sildenafil for both hands and both feet.