Long-Term Follow-up Study of Cantharidin (YCANTH [VP-102/TO-208]) in Patients With Common Warts (Verruca Vulgaris)

People who participated in either the COVE-2 or COVE-3 study for common warts, may be eligible to enroll into this Long Term Follow Up (LTFU) study COVE-4. The main question(s) to answer in this LTFU study are: * To assess the safety of YCANTH (also known as VP-102 in the United Sates or TO-208 in Japan) by assessing concomitant medication use, and adverse events (AEs), including expected local skin reactions (LSRs). * To evaluate the efficacy of continued skin application of YCANTH (VP-102/TO-208) when applied to each common wart once every 21 days for a maximum of 4 additional treatments. Participants with eligible common warts present will receive YCANTH (VP-102/TO-208) with an interval of 21 (± 4) days between applications until there is a wart count of zero (ie, completed clearance has been achieved) or a maximum of 4 additional treatments. Participants with complete clearance will attend Observation Visits at intervals of 42 (± 4) days without treatment. Participants who develop a new wart after having a wart count of zero will resume Treatment Visits every 21 (± 4) days for a maximum of 4 additional treatments. All subjects will attend visits until the End-of-Study (EOS) Visit, which is on Day 378 (0/+ 8 days). If participants still have warts present after 4 additional treatments of YCANTH (VP-102/TO-208) the wart(s) will be discontinued from study and participants will be allowed to seek treatment but should be limited to destructive therapy such as cryosurgery and warts cannot be within 10 mm of any warts that receive(d) study drug treatment . The exact interval of Treatment Visits will be determined by evaluation of the treatment site, taking into account any ongoing local skin reactions (LSRs), which are defined as temporary application site: vesiculation, pain, pruritus, scabbing, erythema, discoloration, dryness, edema and erosion that is expected and consistent with historical treatment with YCANTH (VP-102/TO-208). Participants may receive treatment until all treatable common warts are clear, up to a maximum of 4 treatment sessions, or until Day 357, whichever occurs first. Treatment: For participants with warts present at the time of study entry, the first treatment application may occur on the same day as transition from the parent study. All required parent study assessments must be complete, including the final evaluation of response to treatment (ERT; as defined in Assessments and procedures). In addition, eligibility for participation in the LTFU study must have been determined, and informed consent/assent for participation in this LTFU study obtained. YCANTH (VP-102/TO-208) will be applied by the Investigator or qualified member of the research team to treatable common warts, including an approximate 1 to 2 mm margin of healthy, surrounding skin. After YCANTH (VP-102/TO- 208) is applied, warts are to be covered with occlusive tape (occlusive tape with similar properties should be used across all clinical sites) that will remain in place overnight and should be removed 24 hours after application of study drug and just before a 24-hour ERT. Before application of study drug, wart paring, if necessary, will be completed with a sharp surgical instrument (eg, scalpel or flexible medical blade) to remove any adherent thick scale from a treatable common wart. Wart paring is required to be performed at any treatment visit when adherent thick scale is present, and the Investigator feels paring can be safely performed. Paring should be conducted by a trained practitioner and in compliance with any local regulations and should be discontinued if it results in punctate bleeding or significant pain. Not all treatable common warts may require paring. If adherent scale is not present, study drug can be applied without paring. The assessment for complete clearance may be made once all treatable common warts are evaluable and not obscured by an ongoing LSR. If the Investigator is unable to evaluate or treat 1 or more warts due to ongoing LSRs, no warts should be treated, and the visit will be documented as an Unscheduled Visit. The timing of the next treatment visit will be determined by resolution of the LSRs. The research team will be in contact with the Participant until all LSRs are resolved. Once LSRs have resolved, a Treatment Visit will be scheduled within 21 (± 4) days of the previous treatment application, noting it may be longer than 21 (± 4) days depending on the length of time until LSR resolution. All treatable common warts that are not completely clear should undergo treatment with study drug. Study duration from Days 84, 105, or 147 of the parent study (COVE-2 or COVE-3) through the final EOS visit of this LTFU study (Day 378) is approximately 294 days.