Answer:
A false negative would be a more serious issue. In a false negative result, a woman might be suffering from breast cancer but she will not be diagnosed. As a result, the woman will not take any treatment. This will result for cancer to spread. Cancer might spread to other body parts and might become extremely toxic for the woman. As cancer cannot normally be treated in the later stages, hence diagnosing it later wouldn't help. The woman might die due to the false-negative result.