**Core Concept**
The patient's description of a mole on her upper back with characteristics such as size (6 mm), color (darkly pigmented), shape (asymmetric), and border (irregular) raises concern for a potential skin malignancy, specifically melanoma. The ABCDE rule, a widely used clinical tool for early detection of melanoma, is applicable here.

**Why the Correct Answer is Right**
The ABCDE rule is a mnemonic that helps clinicians identify features of melanoma. A stands for Asymmetry, where one half of the mole does not mirror the other half. B stands for Border, which is irregular, notched, or scalloped. C represents Color, which is usually uneven and may include shades of brown, black, pink, red, white, or blue. D stands for Diameter, which is larger than 6 mm. E stands for Evolving, where the mole changes in size, shape, or color over time. In this case, the patient's mole exhibits all these features, warranting further investigation.

**Why Each Wrong Option is Incorrect**
**Option A:** Excision biopsy is an option, but not the next step, as it would be performed after a definitive diagnosis is made or if the patient is a high-risk individual.
**Option B:** Dermoscopy or epiluminescence microscopy may be useful in the evaluation, but it is not the next step in management for a patient with a suspicious mole.
**Option C:** Mohs surgery is a treatment option for skin cancer, but it is typically reserved for cases where the diagnosis is already confirmed, such as after a biopsy.

**Clinical Pearl / High-Yield Fact**
The ABCDE rule can be remembered by associating each letter with a word that starts with the same sound, such as "Aunt Betty Caught Dysentery Easily." This mnemonic helps clinicians recall the key features of melanoma and perform a thorough examination.

**Correct Answer: B.**