This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urethra & Penis, Subject name: Surgery
What is the most common cause of failure of radiotherapy for stage II cervical carcinoma? 
Select and explain. 
A. Liver metastasis, B. Bone metastasis, C. Para-aortic node metastasis, D. Resistance of the central tumor
C: Para-aortic node metastasis
Answer: C: Para-aortic node metastasis 
Explanation: In stage II cervical cancer, the incidence of nodal involvement is 25%-40%. Most tumors are not radioresistant, and distant metastasis (i.e., a more advanced stage) are a late complication of more advanced stages of the disease.