Which lab test is specifically used for screening breast, lung, and ovarian cancers?

The correct answer is associated with the screening of breast cancer specifically. CA 15-3 is a tumor marker that can be elevated in the presence of breast cancer, making it a useful test in monitoring treatment response and checking for recurrence. While it's not used as a primary screening tool for breast cancer in asymptomatic women, it can provide valuable information in patients who have already been diagnosed.

It's important to note that CA 125 is primarily used in the context of ovarian cancer and can also be elevated in other conditions, including endometriosis and pelvic inflammatory disease. Although elevated levels can indicate the presence of ovarian cancer, it is not specific to breast cancer.

Additionally, both CA 19-9 and CA 27.29 are markers that are relevant in the context of other cancers (such as pancreatic cancer and certain types of gastrointestinal cancers) and do not specifically correlate with breast, lung, or ovarian cancers as effectively as CA 15-3 or CA 125. Thus, CA 15-3 is specifically indicated for breast cancer screening and monitoring, making it the most relevant choice in the context of this question.