Answer:
1. Cancer cells are clonal - True.
2. Benign tumors are invasive - False.
3. Papillomavirus can cause breast cancer in humans - False.
4. Metastatic tumors can invade other tissues - True.
5. Most cancers are the result of exposure to environmental agents - True.
6. Viruses can cause normal cells to be transformed into malignant cells - True.