Assignment
Statement - Ovarian cancer in women is difficult to diagnose in the early stages due to vague symptoms that are commonly experienced by women without ovarian cancer. Most diagnoses are made at an advanced stage where survival is poor. Ovarian cancer has a 5-year survival rate of 46% and there were an estimated 1,075 deaths from ovarian cancer in Australia in 20191. A blood test for the protein CA125, which can be produced by ovarian cancer cells, has been suggested as a screening test for ovarian cancer in older women (aged 50 years or more). A CA125 result greater than or equal to 35 U/mL is considered a positive test. A prospective cohort study was conducted with 78,216 women aged 50 years or more, of whom 388 had ovarian cancer at follow-up, and the remaining 77,828 did not have ovarian cancer according to a gold standard test. The CA125 blood test detected ovarian cancer in 358 of the 388 participants with ovarian cancer. Of the 77,828 participants without ovarian cancer, 75,175 tested negative using CA125.
Task
1. Draw a 2 x 2 table of the results of the CA125 test compared to the gold standard. Label your table appropriately.
2. Calculate the sensitivity of the CA125 test. Show your working.
3. Interpret the value you calculated in part (2).
4. Calculate the specificity of the CA125 test. Show your working.
5. Interpret the value you calculated in part (4).
6. If the threshold for testing positive was reduced (i.e. the cut-off was set lower than 35 U/mL) what impact would this have on sensitivity and specificity? Explain the answer.
7. Considering the values you have calculated in parts 2 and 4, would you recommend its use for population screening? Explain the answer.
8. If a woman in this cohort study had a positive CA125 test how likely is it that they truly have cancer? Show your working and explain the answer.
9. Describe two other factors (other than sensitivity/specificity) that need to be considered to determine whether a routine ovarian cancer screening program should be implemented for women aged 50 years or more.