Following are spontaneous resolution tumours except-a) Malignant melanomab) Osteogenic sarcomac) Cholangio carcinomad) Retinoblastoma

**Core Concept**
Tumor behavior can be broadly classified into two categories: benign and malignant. Malignant tumors are characterized by their ability to invade surrounding tissues, metastasize, and eventually cause death. Spontaneous regression is a rare phenomenon where a tumor, particularly a malignant one, undergoes regression without any treatment.

**Why the Correct Answer is Right**
Spontaneous regression has been observed in various types of tumors, including melanoma, neuroblastoma, and retinoblastoma. This phenomenon is thought to occur due to an imbalance between tumor growth and the host's immune response. In the case of melanoma, spontaneous regression is believed to be the result of an immune-mediated destruction of tumor cells. Retinoblastoma, a type of eye cancer, has also been known to regress spontaneously. The exact mechanisms behind spontaneous regression are not fully understood, but it is thought to involve the body's natural immune response and possibly other factors such as tumor biology and genetics.

**Why Each Wrong Option is Incorrect**
**Option A:** Malignant melanoma is known to exhibit spontaneous regression in some cases, making it an incorrect choice.
**Option B:** Osteogenic sarcoma is a type of bone cancer that is aggressive and typically does not regress spontaneously.
**Option C:** Cholangiocarcinoma is a type of cancer that affects the bile ducts and is known for its poor prognosis, with spontaneous regression being extremely rare.
**Option D:** While retinoblastoma is known to exhibit spontaneous regression, the other options listed are not.

**Clinical Pearl / High-Yield Fact**
Spontaneous regression is a rare phenomenon that highlights the complex interplay between tumor biology and the host's immune response. It serves as a reminder of the body's ability to fight cancer, but also underscores the importance of early detection and treatment to prevent tumor progression.

**Correct Answer:** D. Retinoblastoma