In malignant tumors, the cells proliferate, grow rapidly and move to other parts of the body to form new tumors. This stage of disease is called.

Options

A. metagenesis
B. metastasis
C. teratogenesis
D. mitosis

Answer

### Step-by-Step Solution:

1. **Understanding Tumors**: Tumors are abnormal growths of cells. They can be classified into two main types: benign and malignant.
- **Benign Tumors**: These tumors do not spread to other parts of the body and generally grow slowly.
- **Malignant Tumors**: These tumors are cancerous, grow rapidly, and have the ability to invade other tissues and organs.

2. **Defining the Process**: In malignant tumors, the process by which cancer cells proliferate (multiply) and spread to other parts of the body is crucial to understanding cancer progression.

3. **Identifying the Correct Term**: The specific term for the process of malignant tumor cells moving to other parts of the body to form new tumors is known as **metastasis**. This is a key characteristic of malignant tumors.

4. **Analyzing Other Options**:
- **Metagenesis**: This term relates to the alternation of generations in certain organisms, such as plants and algae, and is not relevant to tumors.
- **Teratogenesis**: This refers to the development of congenital malformations or defects in embryos or fetuses and is not related to tumor spread.
- **Mitosis**: This is a type of cell division that results in two identical daughter cells and does not specifically refer to the spread of cancer.

5. **Conclusion**: Based on the definitions and characteristics discussed, the correct answer to the question is **metastasis**.

### Final Answer:
The stage of disease in malignant tumors where cells proliferate, grow rapidly, and move to other parts of the body to form new tumors is called **metastasis**.

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