DEAR DOCTOR ROACH >> I have recently learned that my sibling, age 70, has rare cancer of the thymus. She will be getting chemotherapy and perhaps radiation treatment. I have heard of immunotherapy. Is this an option?

Would you know what could have caused this type of cancer? When she was younger, she had bouts of rosacea; could there be a connection?

— A.H.

Dear Reader >> The thymus is a gland in the upper chest that is critical for the development of the immune system during early childhood. Tumors of the thymus are rare, and thymic cancer is rarer still. There are no known risk factors for thymic cancer, and rosacea isn’t one to expect.

If the cancer has not spread outside of the thymus, surgery can be curative, but people with high-risk cancers (by pathological evaluation) are usually recommended to follow surgery with radiation treatment. If the cancer has spread, then chemotherapy is the first-line treatment. Some people are cured by chemotherapy, even with advanced disease.

Unfortunately, people with thymic cancer are at a very high risk for serious immune-related side effects from immunotherapy, so this therapy is not helpful in people with thymic cancer.

Because this is such a rare cancer, the optimum treatment isn’t known. I wish her the best in her treatment.

DEAR DR. ROACH >> My 31-year-old daughter is pregnant with her first baby. She is in her fifth month, and the doctor has told her that her baby is at the 75th percentile in growth.

Can you please advise if this is a concern?

— O.G.S.

Dear Reader >> The 50th percentile is, by definition, an average-sized baby (for the appropriate population). The 75th percentile makes her baby a bit bigger than average but, by no means, abnormally large. We start to worry when the baby is above the 90th percentile, although the 95th and 97.75th percentile are commonly used by researchers to define “macrosomia” — a baby who is larger than expected.

When a fetus is that large, there are risks to the mother, including protracted labor, the need for a caesarean birth, and damage to the genital tract and uterus. Risks of a very large baby also include damage to the shoulder during delivery. When a baby is that big, there is a concern that the mother may have high levels of insulin, which acts as a growth hormone for the baby.

Moms who gain excess weight during pregnancy are at a higher risk for larger babies. There are other rare causes. All expectant mothers are screened for the form of diabetes that is associated with pregnancy. A baby born to a mom with diabetes is at risk for low blood sugar when they’re first born.

However, your grandchild is not in a range where any of these bad outcomes are likely. If your daughter or the baby’s father is a large person, there is simply a higher chance that they’ll have a large baby.

On the other side, a developing fetus that is less than the 10th percentile (but especially less than the 3rd percentile) for weight is a bigger concern because there are many worrisome causes for the baby not to grow. Her baby seems to be in a very healthy range.

Finally, the ultrasound pictures aren’t perfect and can under- or overestimate fetal size, so I really wouldn’t get too concerned.  

Contact Dr. Roach at: ToYourGoodHealth@med.cornell.edu.