Major areas of GYN malpractice overlap with cancer malpractice.
Breast Cancer Screening
If the OBGYN is the doctor that's ordering mammograms, then they need to ensure that they're ordered and performed in a timely manner.
They also need to review the results of these and other imaging studies.
If an important finding was not communicated to the patient or important follow up imaging not ordered and performed by the OBGYN, that is malpractice.
Cervical Cancer Screening aka "pap smear"
Likewise, there are very specific algorithms to follow in the screening of cervical cancer.
The official guidelines are through the American Society for Colposcopy and Cervical Pathology.
Failure to adhere to these guidelines is malpractice.