Final answer:
Serum alpha-fetoprotein (AFP) is the tumor marker that is elevated in testicular cancer, which can indicate the presence of the disease and is also used for monitoring after treatment.
Step-by-step explanation:
The correct answer to the question of which tumor marker is elevated in testicular cancer is 4) Serum alpha-fetoprotein (AFP). AFP is considered a tissue-specific marker, which means that its elevated levels can point to specific tissues where cancer may be present. In the context of testicular cancer, if an individual has an elevated level of AFP, a search for testicular cancer will be undertaken.
It's important to note that other markers mentioned, like Carcinoembryonic antigen (CEA) and CA 19-9, are also cancer-specific markers, but they are not primarily associated with testicular cancer. AFP is used not only for the initial detection but also for the monitoring of cancer survivors after treatment, as declining levels usually indicate successful treatment and rising levels can suggest a relapse.