Secondary cancers to the bladder are rare. The majority of them result from direct extension of tumours from surrounding organs, such as prostate, colorectal, and cervical carcinomas; the minority are metastasis originating from lymphoma/leukemias or, less frequently, from solid tumours such as breast, lung and skin primaries.
Differentiating secondary adenocarcinoma lesions from a primary bladder adenocarcinoma can be difficult. In patients without another known primary adenocarcinoma, the possibility of bladder cancer being due to spread of a contiguous-site malignancy should first be sought, but imaging studies of the chest, abdomen, pelvis and bones are also warranted not only for staging but also to rule out the presence of another possible primary malignancy elsewhere. Conversely, in patients known to harbour a distant site primary adenocarcinoma, the differential diagnosis between primary and metastatic bladder adenocarcinoma relies on endoscopic appearance  and pathologic evaluation.
In the few previously reported cases, the finding of an intact epithelium overlying the bladder tumour was considered suggestive of a secondary lesion . Our case is the first jn which the endoscopic appearance was strongly consistent with primary bladder cancer. Such a finding, together with the 13-year history of self clean intermittent catheterization, further complicated the differential diagnosis between metastatic lung adenocarcinoma and primary bladder adenocarcinoma. The differential diagnosis, therefore, had to rely only on a thorough pathologic evaluation.
In the reported case, we elected to use to the TTF-1, CK7, CK20 immunohistochemical panel, which has recently been described as an effective means of differentiating lung adenocarcinoma from its metastases . The use of a limited immunohistochemical panel including napsin A, a recently described highly sensitive marker for lung adenocarcinoma, and GATA3 and S100P, two novel markers of urothelial differentiation, has also been reported to be very useful in differentiating lung adenocarcinoma metastatic to the bladder from primary bladder adenocarcinoma . In our experience, however, the TTF-1-CK7-CK20 panel proved to be easier to apply in routine clinical practice.
In conclusion, the differential diagnosis between secondary bladder cancers and non-transitional cell primary bladder cancers has major clinical relevance as primary bladder cancer is often curable with cystectomy and/or chemotherapy while bladder metastases from other primaries are managed with palliative chemotherapy and have a much worse outcome [7, 8]. An endoscopic appearance consistent with primary bladder cancer, as in the reported case, may further complicate the diagnosis that should, consequently, be based on the patient’s history and, above all, on accurate pathologic evaluation and specific immunohistochemical staining.