A Bit Worried

This .edu site does not mention heredity as a risk factor for cervical cancer http://medicalcenter.osu.edu/patientcare/healthcare_services/gynecological_health/cervical_cancer/pages/index.aspx

nor does the NIH list heredity as a risk factor for cervical cancer. http://understandingrisk.cancer.gov/a_cervical/01.cfm

Only about 10-15% of breast cancers are thought to be due to a single, inheritable gene.  Unless you are of Ashkenazi Jewish heritage, you are probably of low risk for a hereditary breast cancer gene.  Here are the USPTF guidelines for BRCA testing  (BRCA 1 and 2 are probably the most common single inheritable gene mutation) :

Certain specific family history patterns are associated with an increased risk for deleterious mutations in the BRCA1 or BRCA2 gene. Both maternal and paternal family histories are important. For non-Ashkenazi Jewish women, these patterns include 2 first-degree relatives with breast cancer, 1 of whom received the diagnosis at age 50 years or younger; a combination of 3 or more first- or second-degree relatives with breast cancer regardless of age at diagnosis; a combination of both breast and ovarian cancer among first- and second-degree relatives; a first-degree relative with bilateral breast cancer; a combination of 2 or more first- or second-degree relatives with ovarian cancer regardless of age at diagnosis; a first- or second-degree relative with both breast and ovarian cancer at any age; and a history of breast cancer in a male relative.

For women of Ashkenazi Jewish heritage, an increased-risk family history includes any first-degree relative (or 2 second-degree relatives on the same side of the family) with breast or ovarian cancer.

About 2 percent of adult women in the general population have an increased-risk family history as defined here. Women with none of these family history patterns have a low probability of having a deleterious mutation in BRCA1 or BRCA2 genes.

http://www.uspreventiveservicestaskforce.org/uspstf05/brcagen/brcagenrs.htm#clinical

Of the women who do end up getting breast cancer, about 70% of them have no obvious risk factors (besides being a woman.)

So, unless you are of Ashkenazi Jewish heritage, you are probably NOT at increased risk for breast cancer or cervical cancer due to heredity. Because the parent in common did NOT have a history of cancer, it sounds like it is unlikely that you are of increased risk from hereditary causes.

One thing that has been related with both breast cancer and cervical cancer is DES exposure. Do you share the same mother? Did she take DES during one or both of your pregnancies?