Per the ICD-10 guidelines, facilities may code uncertain diagnoses for inpatient claims only, physician or outpatient facility may not: "Do not code diagnoses documented as “probable”, “suspected,” “questionable,” “rule out,” or “working diagnosis” or other similar terms indicating uncertainty. Rather, code the condition(s) to the highest degree of certainty for that encounter/visit, such as symptoms, signs, abnormal test results, or other reason for the visit."
If the physician has documented that they 'think' it is prostate cancer, that is an indication of uncertainty and shows that the provider is using it as a working diagnosis rather than a confirmed diagnosis, and it would not be appropriate to code a prostate cancer. If, however, the physician has documented they have actually diagnosed the patient with cancer, but the documentation does not reflect that the diagnosis has been confirmed with a pathology report, I would either query the physician for clarification or refer the encounter to a supervisor, because to my knowledge it is not possible for a physician to render a diagnosis of a malignancy without a pathology report. I don't know of any documentation to support this rule, but considering the severity and implications of this kind of a diagnosis, it requires a special kind of attention and is important to get this one correct.