Final answer:
Based on the family history and the prevalence of certain mutations, it is likely that breast cancer in Rebecca's family is hereditary.
Step-by-step explanation:
Based on the information provided in the case study, the high incidence of cancers in Rebecca's family, including breast and ovarian cancer, indicate a possible hereditary component. The presence of these cancers in multiple relatives, particularly at an early age, and their relationships to each other in the family pedigree suggest that there may be mutations in certain genes, such as BRCA1 and BRCA2, that increase the risk of getting cancer. Additionally, the prevalence of these mutations in people of Ashkenazi Jewish descent, like Rebecca, further supports the possibility of hereditary breast cancer in her family.