Primary thyroid-like follicular renal carcinoma: a clinical case and literature review

Primary thyroid-like follicular renal cell carcinoma is an extremely rare type of renal cell cancer with low malignancy potential and relatively good prognosis. It has not been included into the World Health Organization classification of renal tumors. This tumor is characterized by morphology similar to primary thyroid follicular cancer, but with different immune phenotype, which is important for morphological diagnosis. Surgery has been recognized as the only curative treatment. We describe our own observation of follicular renal carcinoma in a 68-year old man, in whom renal tumor was identified during his regular examination due to past colon cancer. The disease was asymptomatic. The patient had elective laparoscopic nephrectomy. At pathological assessment, the tumor looked like a follicular thyroid neoplasm. Immunohistochemistry revealed no expression of RCC, TTF-1, thyroglobulin, CD-10, synaptophysin, and chromogranin A. The differential diagnosis included metastatic primary thyroid malignancy as the most probable diagnosis, as well as highly differentiated neuroendocrine tumor and the so-called “thyroid kidney” that might occur in long-standing chronic pyelonephritis. Conclusion: The case of primary follicular renal carcinoma illustrates that this rare renal tumor is heterogeneous both in its structure and tumor cell immunophenotypes. Longer follow-up and accumulation of larger numbers of the disease is needed. This would allow for a more objective assessment of its prevalence in the population, of its clinical characteristics and morphological variability.