Study to Evaluate the Efficacy and Safety of P-3073 Nail Solution in the Treatment of Mild to Moderate Psoriatic Fingernail/s

This phase III study versus vehicle will be conducted to confirm the clinical efficacy and safety of P-3073 in patients affected by isolated psoriatic nail(s) and/or those with psoriatic nails and concomitant mild-to-moderate plaque psoriasis. The evaluation of the primary endpoint will be made using the Nail Psoriasis Severity Index (NAPSI). The secondary objectives will be: * To assess if the topical treatment with P-3073 is able to improve the quality of life and discomfort in patients with psoriatic fingernail. * To assess the safety and tolerability of topical P-3073 in the treatment of psoriatic fingernail. The study consists of two arms comparing P-3073 (calcipotriene 0.005%) and vehicle. Eligible patients will be randomized to either P-3073 or placebo in a 1:1 ratio, stratified by their target nail NAPSI severity at screening. The study population will include at least 470 patients (235 for each group) with nail psoriasis (fingernails) of the matrix and/or of the nail bed in at least one fingernail. The total duration of the trial for each patient will be approximately 29 weeks (from Screening to Follow-up). During the 24 weeks of the treatment period, patients will apply the assigned treatment to all affected psoriatic fingernails once daily.