Skin biopsy of a patient shows evidence of malignant melanoma. Which is the common type of malignant melanoma?
First, I remember that there are several subtypes of melanoma. The main ones are superficial spreading melanoma, nodular melanoma, lentigo maligna melanoma, and acral lentiginous melanoma. Also, maybe a few others like desmoplastic or mucosal melanomas.
Superficial spreading melanoma is the most common in fair-skinned populations. It's characterized by radial growth phase, spreading horizontally before vertical spread. Nodular melanoma is more aggressive, growing vertically from the start. Lentigo maligna is associated with sun damage, often on older adults. Acral lentiginous is on palms, soles, or under nails, and more common in darker-skinned individuals.
So the correct answer should be superficial spreading melanoma. The options might have these as choices. The other options would be the other types. Need to explain why each is incorrect. For example, nodular is aggressive but less common. Lentigo maligna is less common and in older adults. Acral is rare in fair-skinned people.
Clinical pearl: Superficial spreading is most common, followed by nodular. Remember ABCDE criteria for melanoma. High-yield fact for exams.
**Core Concept**
Malignant melanoma has four major subtypes, with superficial spreading melanoma being the most common in fair-skinned populations. It is characterized by radial growth and typically presents on the trunk or extremities.
**Why the Correct Answer is Right**
**Superficial spreading melanoma** accounts for ~70% of all melanoma cases. It arises from preexisting nevi or de novo lesions, initially spreading horizontally (radial growth phase) before vertical invasion. Histologically, it shows irregular nests of atypical melanocytes at the dermo-epidermal junction.
**Why Each Wrong Option is Incorrect**
**Option A:** *Nodular melanoma* is aggressive but accounts for ~15-20% of cases. It grows vertically from onset, lacking a radial phase.
**Option B:** *Lentigo maligna melanoma* is linked to chronic sun exposure, common in elderly patients, and constitutes <5% of cases.
**Option C:** *Acral lentiginous melanoma* occurs on palms/soles/nails, is rare in fair-skinned individuals, and comprises 6mm, Evolving) for clinical suspicion. Nodular melanoma is often mistaken for a benign nodule, leading to delayed diagnosis.
**Correct Answer: B. Superficial Spreading Melanoma**