Transitional cell carcinoma of the bladder mimicking lobular carcinoma of the breast: a discohesive variant of urothelial carcinoma

AIMS: To describe a series of 10 cases of transitional cell carcinoma which show morphological features which mimic lobular carcinoma of the breast and diffuse carcinoma of the stomach. METHODS AND RESULTS: Ten cases were identified from the files at Southampton University Hospitals NHS Trust and from the authors' consultation files. Immunostains were performed and clinical information was obtained. Eight of the patients were male and two female. Ages ranged from 52 to 77 years at presentation. All of the tumours showed areas where the tumour was composed of uniform cells with a discohesive single-cell, diffusely invasive growth pattern. In areas the tumour cells were arranged in linear single-cell files and in separate areas solid sheets of discohesive cells. In all of the cases some tumour cells showed prominent intracytoplasmic vacuoles. In addition to this pattern, four cases showed typical transitional cell carcinoma or carcinoma in situ. The majority of the tumours expressed cytokeratin 20 but not oestrogen receptors. CONCLUSION: This study highlights a pattern of diffusely invasive transitional cell carcinoma not previously described and one which is important to recognize in order to avoid misdiagnosis of metastatic lobular carcinoma of the breast, especially in small biopsies.