**Question:** Spontaneously regressing tumours are

A. benign
B. malignant
C. immunologically mediated
D. associated with a poor prognosis

**Core Concept:** Spontaneously regressing tumours are a subset of neoplasms that shrink or disappear without conventional therapeutic intervention. They can be benign (non-cancerous) or malignant (cancerous) tumours. However, in this case, the focus is on the underlying mechanism driving the regression.

**Why the Correct Answer is Right:** The correct answer, C. immunologically mediated, refers to a specific type of spontaneously regressing tumours where the immune system plays a crucial role in eliminating the tumour cells. This mechanism involves immune cells and cytokines recognizing and attacking the tumour cells, leading to tumour regression.

**Why Each Wrong Option is Incorrect:**

A. Benign (non-cancerous) tumours can regress spontaneously, but the question pertains to tumours exhibiting regression without mentioning the type.

B. Malignant (cancerous) tumours rarely regress spontaneously, as they often possess genetic mutations and uncontrolled cell division, making them more resistant to immune-mediated regression.

D. Associating regressing tumours with a poor prognosis is incorrect, as some tumours can spontaneously regress, leaving the patient without the need for extensive treatment.

**Clinical Pearl:** Immunologically mediated spontaneous regression of tumours is a fascinating phenomenon seen in certain tumour types, such as in melanoma and renal cell carcinoma, which can be attributed to the host's immune response against the tumour cells. Understanding these mechanisms is essential for practicing oncologists and residents in the field of cancer medicine.