**Core Concept**
Mohan's or Mohs surgery is a precise, tissue-sparing surgical technique used for the removal of skin cancers, particularly those that are aggressive or have a high potential for recurrence. This procedure involves the removal and examination of the tumor in thin layers, allowing for the preservation of as much healthy tissue as possible.

**Why the Correct Answer is Right**
In Mohs surgery, the tumor is removed in thin layers, and each layer is examined microscopically for the presence of cancer cells. This process is repeated until no cancer cells are found in the final layer, ensuring the complete removal of the tumor while preserving as much healthy tissue as possible. The technique is particularly useful for treating tumors in cosmetically sensitive areas, such as the face, where preserving tissue and minimizing scarring is crucial.

**Why Each Wrong Option is Incorrect**
* **Option A:** Mohs surgery is not primarily used for the treatment of benign lesions, as it is a technique that is specifically designed to remove and diagnose cancer cells.
* **Option B:** While Mohs surgery can be used to treat a variety of skin cancers, it is not the primary treatment for melanoma, as this type of cancer often requires more aggressive treatment.
* **Option C:** Mohs surgery is not a treatment for systemic diseases, but rather a localized surgical technique used to remove skin tumors.

**Clinical Pearl / High-Yield Fact**
Mohs surgery is often referred to as the "gold standard" for the treatment of skin cancers, particularly those that are aggressive or have a high potential for recurrence. This is due to its high success rate and ability to preserve as much healthy tissue as possible.

**Correct Answer:** D.