At the time of the examination, the twins were 52 years old. In their early decades of life, they lived in multiple regions of the country because their father was an active-duty military officer with rotating assignments. Both twins' third through fifth decades of life were spent in the same town in Tennessee; in the year before the examination, twin 1 relocated to a town 60 miles south of twin 2. Twin 1 reported a medical history significant for tonsillectomy, hysterectomy, vertebral disk herniation, and recently diagnosed hypertension; twin 2 also reported a hysterectomy, as well as a cholecystectomy and degenerative joint disease. Neither twin had a documented history of any skin disease, including skin cancer. Both twins recounted having “frequent sunburns that were red and tender but not blistered” during their childhood. Both twins reported “somewhat regular” sun exposure during adulthood (on a scale of 0 [never] to 4 [very regularly]) because they both had worked as drivers for a delivery service for approximately 10 years. In addition, they never spent time in the sun trying to get a tan (on a scale of 0 [never] to 4 [very regularly]) and never used a tanning bed during adulthood (on a scale of 0 [never] to 4 [very regularly]). When they were in the sun without sunscreen, twin 1 reported that her skin burns moderately and tans gradually and twin 2 reported that her skin always burns easily and tans a little (on a scale of 0 [always burns easily, never tans] to 5 [never burns]). Within the preceding year, twin 2 had started using a daily moisturizer with a sun protection factor of 15, whereas twin 1 used no skin care products. Neither reported use of a topical retinoid. Both twins reported minimal to no alcohol consumption, no routine exercise (on a scale of 1 [yes] to 2 [no]), and described themselves as very overweight (on a scale of 1 [very underweight] to 5 [very overweight]). Twin 1 was a cigarette smoker with an approximately 52.5–pack-year history, whereas twin 2 was a nonsmoker and had never smoked.