Final answer:
In cancer survivor monitoring, an elevated alpha-fetoprotein level in a child previously treated for teratoma may indicate a relapse with an endodermal sinus tumor.
Step-by-step explanation:
The monitoring of cancer survivors after treatment is crucial for early detection of relapse. An example of this is the use of biomarkers such as alpha-fetoprotein (AFP). In children who have been treated for a teratoma, an elevated AFP level could suggest a relapse with an endodermal sinus tumor, also known as yolk sac tumor. This is why post-treatment surveillance using appropriate biomarkers is an integral part of the management strategy for cancer survivors.