Which histological type of uveal malignant melanoma has worst prognosis?
**Core Concept**
Uveal malignant melanoma is a type of cancer that arises from the pigment cells (melanocytes) of the uvea, the middle layer of the eye. The prognosis of uveal melanoma depends on various factors, including the histological type, which refers to the microscopic appearance of the tumor.
**Why the Correct Answer is Right**
The worst prognosis among the histological types of uveal melanoma is associated with the spindle B cell type. This type of melanoma has a higher tendency to spread to distant organs, such as the liver, and has a poorer response to treatment. The spindle B cell type is characterized by a mixture of spindle-shaped cells and epithelioid cells, with a higher nuclear-to-cytoplasmic ratio and more mitoses, indicating a higher proliferation rate.
**Why Each Wrong Option is Incorrect**
**Option A:** The epithelioid cell type has a generally worse prognosis than the spindle A cell type, which is associated with a better prognosis due to its lower nuclear-to-cytoplasmic ratio and fewer mitoses.
**Option B:** The spindle A cell type is associated with a better prognosis than the spindle B cell type, due to its lower nuclear-to-cytoplasmic ratio and fewer mitoses.
**Option C:** The mixed cell type is not typically associated with the worst prognosis among the histological types of uveal melanoma.
**Option D:** The necrotic cell type is not a recognized histological type of uveal melanoma.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the prognosis of uveal melanoma is highly dependent on the histological type, and the spindle B cell type is associated with the worst prognosis. This is a critical piece of information for ophthalmologists and oncologists to consider when managing patients with uveal melanoma.
**Correct Answer:** C.