This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Oral Cavity, Subject name: Surgery
The prognosis for squamous carcinoma of the floor of the mouth is adversely affected by which of the following?Composite resection specimen of a T4 floor of mouth squamous cell carcinoma 
Select and explain. 
A. Poor differentiation of tumor, B. Nonverrucous carcinoma, C. Presence on left side, D. No tongue involvement
A: Poor differentiation of tumor
Answer: A: Poor differentiation of tumor 
Explanation: Poorly differentiated squamous cell carcinoma of the floor of the mouth tends to be more invasive than better-differentiated tumors. Poorer prognosis can be expected when invasion is larger than 9 mm, perineural invasion is noted, and lymph node metastasis is evident.