This will be a dose escalation study to determine the maximum tolerated dose (MTD) and the overall safety and tolerability of a topical compound 31543 (Calcitriol) in patients with metastatic or recurrent cancer who are undergoing chemotherapy with a taxane-based regimen. A standard 3+3 dose escalation design will be employed with 3-6 patients at each dose level. Eligible patients ≥18 years of age and scheduled to receive a taxane-based regimen with treatment breaks as per physician's discretion, will start applying the topical solution twice a day at each cohort dose level two weeks or 7 days ± 2 days prior to initiation of chemotherapy and then continue twice daily for 3 months or until termination of chemotherapy treatment. If topical calcitriol is found to be effective in preventing and/or diminishing taxane chemotherapy-induced alopecia as determined by the photographic assessments and patient self-assessments, patients will be allowed to continue topical application for the duration of their chemotherapy treatment, assuming no dose limiting toxicities (DLTs) related to the topical agent or intolerable side effects are observed. Toxicity to the topical compound 31543 (calcitriol) will be assessed on a weekly basis during the first 28 days of topical treatment and subsequently every four weeks by a study clinician, either a physician or a nurse. For the purpose of pharmacokinetic studies (PKs), blood samples will be collected on Day 1 of topical treatment at the following time points: pre-dose, at 2 hrs (±30 minutes), 4 hrs (±30 minutes), and 8 hrs (±1 hr post dose) after a single application on the morning of Day 1. The second application of drug product will be applied 10-14 hrs after the initial application and after the 8 hr PK sample. Thereafter, topical application frequency will be twice daily, morning and night. Subsequently, a PK sample will be taken 12 hrs (±2 hrs) after the last dose of each 28-day treatment, before the first application of Day 1 of the next 28-day treatment cycle. This schedule will continue for three consecutive 28-day topical treatment cycles. (PKs will be drawn at Weeks 1, 5, 9, and 13. In addition, if patients are still on study, a PK will also be drawn at Week 54.) As a secondary objective, potential efficacy of the topical calcitriol will be evaluated by photographic assessment. Photographic assessment will be performed using a Canon digital camera system to ensure standardization and uniformity among all enrolled patients. The following five views will be obtained at each photographic assessment: bilateral sides of head/scalp view, front of head/face view, back of head/scalp view, and top of head/scalp view.Additionally, close-up photographs will be taken at the same time points. They will include the mid-pattern of the scalp from a superior view and a vertex view with hair parted in the center and combed away from the center part. Photographs will be standardized for lighting, camera angle, and position to the participant's head.These assessments will be performed at the following time points: at baseline, Weeks 7, 15, 27, and 54. Photographs for patients in each cohort representing baseline, and treatment Weeks 7 and 15 will be presented blind to the study PI and dermatologist, Mario Lacouture, after at least 3 patients have completed 15 weeks of treatment. Photographs will also be taken at Week 27 and Week 54 of the study but will be included in the final photographic assessment as secondary information. In addition, all patients will be asked to maintain an application log throughout treatment to ensure compliance.

Additionally patients will maintain a medication application diary and a self-assessment diary. The medication application diary will collect daily application details of the medication. This will include application dates and times, chemotherapy cycle, and whether the medication was applied (or reason if the medication was not applied). The self-assessment diary will require assessment of hair thickness, hair fullness, hair breakage, and hair cosmetic qualities (ease of styling, etc.) on an analog 10 point scale to assess patient-reported efficacy. The PI clinical assessment of baseline, Weeks 7 and 15 photographs will be used, together with the patient diary information, for the primary assessment of alopecia. The study is expected to take place over a period of approximately 12 months, including the screening period.