A Multi-Center Study to Evaluate the Efficacy and Safety of KX2-391 Ointment 1% on Actinic Keratosis on Face or Scalp (AK004)

Inclusion Criteria 1. Males and females greater than or equal to (\>=) 18 years old. 2. A defined area on the face or scalp contains 4 to 8 clinically typical, visible, and discrete AK lesions. 3. Participants who in the judgment of the Investigator, were in good general health. 4. Females were postmenopausal (greater than \[\>\] 45 years of age with at least 12 months of amenorrhea), surgically sterile (by hysterectomy, bilateral oophorectomy, or tubal ligation); or, if of childbearing potential, were using highly effective contraception for at least 30 days or 1 menstrual cycle, whichever was longer, prior to study treatment and agreed to continue to use highly effective contraception for at least 30 days following their last dose of study treatment. Highly effective contraception includes oral hormonal contraceptives, hormonal contraceptive implant, injection or patch, intrauterine device or complete abstinence from sexual intercourse. 5. Sexually active males who had not had a vasectomy, and whose partner was reproductively capable, must had agreed to use barrier contraception from Screening through 90 days after their last dose of study treatment. 6. All participants must had agreed not to donate sperm or eggs or attempt conception from Screening through 90 days following their last dose of study treatment. 7. Willing to avoid excessive sun or ultraviolet exposure. 8. Able to comprehend and were willing to sign the informed consent form (ICF). Exclusion Criteria 1. Clinically atypical and/or rapidly changing AK lesions on the treatment area. 2. Location of the selected area is: * On any location other than the face or scalp. * Within 5 centimeters (cm) of an incompletely healed wound. * Within 5 cm of a suspected basal cell carcinoma (BCC) or squamous cell carcinoma (SCC). 3. Been previously treated with KX2-391 Ointment. 4. Anticipated need for in-patient hospitalization or in-patient surgery from Day 1 to Day 57. 5. Treatment with 5-fluorouracil (5-FU), imiquimod, ingenol mebutate, diclofenac, photodynamic therapy, or other treatments for AK within the treatment area or within 2 cm of the treatment area, within 8 weeks prior to the Screening visit. 6. Use of the following therapies and/or medications within 2 weeks prior to the Screening visit: * Cosmetic or therapeutic procedures (e.g., use of liquid nitrogen, surgical excision, curettage, dermabrasion, medium or greater depth chemical peel, laser resurfacing) within the treatment area or within 2 cm of the selected treatment area. * Acid-containing therapeutic products (eg, salicylic acid or fruit acids, such as alpha- and beta-hydroxyl acids and glycolic acids), topical retinoids, or light chemical peels within the treatment area or within 2 cm of the selected treatment area. * Topical salves (non-medicated/non-irritant lotion and cream were acceptable) or topical steroids within the treatment area or within 2 cm of the selected treatment area; artificial tanners within the treatment area or within 5 cm of the selected treatment area. 7. Use of the following therapies and/or medications within 4 weeks prior to the Screening visit: * Treatment with immunomodulators (eg, azathioprine), cytotoxic drugs (eg, cyclophosphamide, vinblastine, chlorambucil, methotrexate) or interferons/interferon inducers. * Treatment with systemic medications that suppress the immune system (eg, cyclosporine, prednisone, methotrexate, alefacept, infliximab). 8. Use of systemic retinoids (eg, isotretinoin, acitretin, bexarotene) within 6 months prior to the Screening visit. 9. A history of sensitivity and/or allergy to any of the ingredients in the study medication. 10. A skin disease (e.g., atopic dermatitis, psoriasis, eczema) or condition (e.g., scarring, open wounds) that, in the opinion of the Investigator, might interfere with the study conduct or evaluations, or which exposes the participant to unacceptable risk by study participation. 11. Other significant uncontrolled or unstable medical diseases or conditions that, in the opinion of the Investigator, would expose the participant to unacceptable risk by study participation. 12. Females who were pregnant or nursing. 13. Participated in an investigational drug trial during which an investigational study medication was administered within 30 days or 5 half-lives of the investigational product, whichever was longer, before dosing.