Thesis = subtopic 1 + subtopic 2 + subtopic 3
or more specifically for your thesis...
Thesis = cause/effect 1 + cause/effect 2 + cause/effect 3
Words you can use to indicate causes: factor, basis, reason, source, root, origin
Words you can use to indicate an effect: result, consequence, impact, outcome, upshot, resulting symptoms, etc...
Broad topic: cancer
Narrower topic: breast cancer
Even narrower topic: causes and effect of breast cancer
Thesis = For the thousands who are diagnosed with breast cancer annually, the following factors are significant issues: symptoms of early onset, physiological causes, and the broad variety of effects from the disease.