Chronic inflammation is a hallmark of cancer [55–58] and at 52 weeks hyperplasia was observed in the lungs of the 0.25 and 0.50 mg DWCNT treated rats and at 104 weeks the alveolar PCNA index was elevated in all DWCNT treated rats and tumor incidence was significantly increased the rats administered 0.5 mg DWCNT. Here, PCNA is linked to cancer.