1.1. State and explain three reasons why malignant tumours are considered more harmful than benign tumours.

1.2. Oestrogen is a hormone which is thought to play a role in the increased risk of breast cancer in post-menopausal women. Oestrogen only affects target cells, mainly those in the breast tissue.

Explain how an increase in oestrogen levels may lead to the development of breast cancer.

1.3. Tamoxifen is a drug that has been used to help prevent and treat breast cancer by blocking the effects of oestrogen in the breast tissue. Scientists developing treatment for breast cancer completed a trial on mice to compare an alternative drug called Anastrozole with Tamoxifen.

Anastrazole works by inhibiting an enzyme called aromatase which is responsible for the production of oestrogen in post-menopausal women.

The scientists first removed the ovaries from the mice, then they injected them with tumour causing chemicals found in tobacco twice a week for 3 weeks. After week 3, the mice were given the drugs for a further 10 weeks.

The mice were then randomly allocated to 1 of 3 groups, each with 20 mice:

• Group A was given a placebo

• Group B was given the drug anastrozole

• Group C was given the drug tamoxifen

The scientists removed the ovaries from the mice and injected them daily with Aromatase. Explain why these stages were necessary.

1.4. The results of the investigation can be seen in Figure 1.

Figure 1

The scientists concluded that Anastrozole was the most effective at controlling tumour growth due to oestrogen.

Use the data shown in Figure 1 to evaluate this claim.