**Question:** All are growth promoting oncogenes except -

A. **Neurofibromatosis type 1 (NF1)**
B. **Neurofibromatosis type 2 (NF2)**
C. **Retinoblastoma (Rb)**
D. **Polyposis coli (PC)**

**Core Concept:**

Oncogenes are a class of genes that, when mutated or overexpressed, can cause uncontrolled cell growth, leading to the development of cancer. There are two types of oncogenes: **tumor suppressor genes** and **growth promoting oncogenes**. Tumor suppressor genes, like NF1 and NF2, help regulate cell growth and prevent uncontrolled cell division. When mutated, they can contribute to cancer development. Growth promoting oncogenes, as the name suggests, promote cell growth and division, which can also lead to cancer formation.

**Why the Correct Answer is Right:**

Neurofibromatosis type 1 (NF1) and Neurofibromatosis type 2 (NF2) are examples of **tumor suppressor genes**. Mutations in these genes cause the loss of their tumor suppressor function, leading to uncontrolled cell growth and the development of neurofibromas and schwannomas, respectively. These genes are not growth promoting oncogenes, but rather play a role in preventing uncontrolled cell growth.

**Why Each Wrong Option is Incorrect:**

Neurofibromatosis type 1 (NF1) and Neurofibromatosis type 2 (NF2) are **tumor suppressor genes**, not growth promoting oncogenes. In contrast, growth promoting oncogenes promote cell growth and division, contributing to cancer development.

**Retinoblastoma (Rb)** and **Polyposis coli (PC)** are examples of **growth promoting oncogenes**. Retinoblastoma (Rb) is a gene responsible for regulating cell cycle progression and preventing uncontrolled cell growth. Mutations in this gene can lead to the development of retinoblastoma, a type of eye cancer. Polyposis coli (PC) is a genetic disorder that predisposes individuals to develop colon polyps and eventually colorectal cancer due to mutations in the APC gene, which is involved in regulating cell growth and differentiation.

**Clinical Pearls:**

1. **Neurofibromatosis type 1 (NF1) and Neurofibromatosis type 2 (NF2)** are genetic disorders that result from mutations in tumor suppressor genes, not growth promoting oncogenes. Tumor suppressor genes like NF1 and NF2 serve to prevent uncontrolled cell growth and division, and their mutations lead to unregulated cell proliferation, which can cause cancer.
2. **Retinoblastoma (Rb)** and **Polyposis coli (PC)** are examples of growth promoting oncogenes. Mutations in Rb and PC genes lead to unregulated cell growth and division, contributing to the development of cancer.

**Why the Correct Answer is Rb and PC:**

The correct answer is Rb and PC because these are growth promoting oncogenes that