Ariande - nicely done
There are also the genetic factors; a mutation in the BRCA1 gene, for example, leaves you much more prone to a certain type of breast and ovarian
cancer.
Then there are cancers triggered by virii - one of the HPV family of virii causes cervical cancer; the Eppstein-Barr virus has been associated with
several cancers, including Burkitt's Lymphoma and nasopharyngeal carcinoma.
To say that we all "have" cancer is sort of true, as Ariande said....but only in as much as we all have cells which in turn have the potential to
become cancerous....and it's not the same as thinking "we all have secret cancers inside us just waiting to explode".
There are no guarantees, unfortunately. You could have both ovaries removed and still become a victim of ovarian cancer; likewise, whilst a double
mastectomy reduces the likelihood, it cannot rule out your getting breast cancer.
Sometimes, things happen for no apparent reason.