1.1. Neuroblastoma is a cancer of the nervous system. A characteristic feature of neuroblastoma cells is the high expression of a surface antigen called GD2, which is present at much lower levels on normal cells.

Scientists investigated a combination therapy using 2 drugs:

1. Anti-GD2 mAbs: specially designed monoclonal antibodies

2. Vorinostat: an inhibitor of histone deacetylase (HDAC), an enzyme that normally reduces gene expression

Mice with neuroblastoma were divided into four groups:

1. control

2. treated with anti-GD2 mAbs only

3. treated with Vorinostat only

4. treated with Vorinostat + anti-GD2 mAbs

Survival of the mice was recorded over time and the results are shown in Figure 5.

Figure 5

Compare the effect of the different treatments on mouse survival.

1.2. Suggest how anti-GD2 mAbs can lead to the destruction of tumour cells.

1.3. Using Fig. 5, estimate the median survival time for mice treated with both anti-GD2 antibodies and Vorinostat.

1.4. Suggest one limitation of using this graph to determine median survival time.