This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Which of the following features cannot be used to differentiate between Hodgkin's and Non Hodgkin's Lymphoma ? 
Select and explain. 
A. Extranodal involvement, B. Spread contiguity, C. Painless lymphadenopathy, D. Localisation to a particular group of lymph nodes
C: Painless lymphadenopathy
Answer: C: Painless lymphadenopathy 
Explanation: Hodgkin lymphoma, like NHL, usually manifests as painless lymphadenopathy.  Although a definitive distinction from NHL can be made only by examination of a tissue biopsy,  several clinical features favor the diagnosis of Hodgkin lymphoma. After the diagnosis is established, staging is used to guide therapy and determine prognosis.