Not only positive but also negative control can be taken for better analysis. Samples can be obtained from the concerned Cancer Hospital. Cooperation of the Oncopathologists is essential.

I assume you are trying to evaluate the role of tumor associated macrophages in OSCC. From what I have deducted from the literature, I feel you can use any periapical inflammatory lesions as a positive control like periapical granuloma or radicular cyst. I think these lesional tissues would be readily available in your university. Do some more literature review before going ahead with the control selection. And any non inflammed oral mucosal tissue can be used as a negative control.