Evaluate the safety, tolerability of A-101 when applied to seborrheic keratosis lesions on the back of subjects.

The main objective of this study is to evaluate the safety, effectiveness and tolerability of three concentrations of A-101 25%, 32.5%, and 40%, when applied to individual seborrheic keratosis target lesions on the back compared with a matching A-101 vehicle.

Inclusion Criteria:

1. Is at least 18 years of age
2. Has a clinical diagnosis of stable clinically typical seborrheic keratosis
3. Has at least 4 appropriate seborrheic keratosis target lesions on the back
4. If subject is a women of childbearing potential, she must have a negative urine pregnancy test and must agree to use an active form of birth control for the duration of the study
5. Is non-pregnant and non-lactating
6. Is in good general health and free of any disease state or physical condition which, in the investigator's opinion, might impair evaluation of any target lesion or which exposes the subject to an unacceptable risk by study participation
7. Is willing and able to follow all study instructions and to attend all study visits
8. Is able to comprehend and willing to sign an Informed Consent Form (ICF).

Exclusion Criteria:

1. Has clinically atypical and/or rapidly growing seborrheic keratosis lesions

2. Has presence of multiple eruptive seborrheic keratosis lesions (Sign of Leser-Trelat)

3. Has used any of the following systemic therapies within the specified period prior to Visit 1:

   • Retinoids; 180 days
   • Glucocorticosteroids; 28 days
   • Anti-metabolites (e.g., methotrexate); 28 days

4. Has used any of the following topical therapies on the treatment area within the specified period prior to Visit 1:

   • Retinoids; 90 days
   • Liquid nitrogen, electrodesiccation, curettage, imiquimod, 5-fluorouracil, or ingenol mebutate; 60 days
   • Glucocorticosteroids or antibiotics; 14 days
   • Moisturizers/emollients, sunscreens; 12 hours

5. Has had any LASER, light (e.g., intense pulsed light (IPL), photo-dynamic therapy (PDT)) or other energy based therapy on the treatment area within 180 days prior to Visit 1

6. Has a history of keloid formation or hypertrophic scarring

7. Has a current systemic malignancy

8. Has a history of, within the 180 days prior to Visit 1, or has a current cutaneous malignancy on the treatment area

9. Has a current pre-malignancy (e.g., actinic keratosis) on the treatment area

10. Has had body art (e.g., tattoos, piercing, sculpting, etc.) or any other invasive, non-therapeutic procedure performed on the treatment area that, in the opinion of the investigator, might put the subject at undue risk or interfere with the study conduct or evaluations

11. Has excessive tan on the treatment area that, in the opinion of the investigator, might put the subject at undue risk or interfere with the study conduct or evaluations

12. Has experienced a sunburn on the treatment area within the previous 4 weeks

13. Has a history of sensitivity to any of the ingredients in the study medications

14. Has any current skin disease (e.g., psoriasis, atopic dermatitis, eczema, sun damage, etc.), or condition (e.g., sunburn, tattoos, excessive hair, open wounds on the back) that, in the opinion of the investigator, might put the subject at undue risk or interfere with the study conduct or evaluations

15. Has participated in an investigational drug trial in which administration of an investigational study medication occurred within 30 days prior to Visit 1.

Serious adverse events were collected from the time the subject signed the informed consent until the subject's last visit. Adverse events were collected from the time immediately after the first application of the study medication until the subject's last visit.

Since each patient simultaneously participates in all four treatment groups only skin site related adverse events are reported by treatment group. Systemic adverse events are reported in all treatment groups the same.