OIN/CIS can sometimes be difficult to distinguish pathologically from epithelial dysplasia on hematoxylin- and eosin-staining sections; this has proved challenging for oral pathologists [9]. Recently, it has been reported that combined immunohistochemistry for k13 and k17 was useful for the differential diagnosis [9, 10]. K13 is a marker for cellular differentiation toward prickle cells in normal stratified squamous epithelia, and its loss or attenuation is observed in oral SCC. Conversely, k17 is not expressed in normal stratified squamous epithelia or specifically localized in SCCs. Our case showed a partial reduction in k13 expression and a mosaic-like pattern as well as being positive for k17 expression, leading to a diagnosis of OIN /CIS.

In the irreversible multistep carcinogenesis, most cases of invasive oral SCC that break through the basement membrane develop as the next pathological stage into OIN/CIS following severe epithelial dysplasia. Such precancerous lesions are clinically observed to be leukoplakic, erythroplakic, or a combination of these. Oral SCCs are frequently accompanied by such precancerous lesions which spread out around them.

Raiser et al. [8] reviewed 42 cases of oral malignancy in which dental implants were implicated, retrieved from a literature search of PubMed and Google Scholar. From the analysis, the affected individuals tend to be elderly adults (mean age, 68 years). The gender distribution shows a clear 1:1.5 female predominance opposed to the characteristic male predominance of oral cancer in general. They also found that 45.3% of cases occurred in a population with recognized risk factors for oral cancer; in addition, 47.5% of cases had experienced a previous oral malignancy, and 19% exhibited the histology of a non-oral malignancy that could metastasize to the jaws or gingiva. Our patient did not have any of the recognized risk factors for oral cancer, including a tobacco-smoking habit or heavy alcohol consumption, nor were further predisposing factors for oral cancer, such as a precancerous lesion or previous oral cancer observed in her oral cavity, including around the OIN/CIS lesion. Thus, she did not fit with the concept of “field cancerization” in the development of oral cancer, which has been accepted by most oral pathologists since being proposed in 1953 by Slaughter et al. [11].