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Abstract Backgrounds Although calcifications have been observed in various renal masses, osseous metaplasia has very rarely been reported. Here, we present a case of concomitant clear cell renal cell carcinoma with osseous metaplasia and papillary thyroid microcarcinoma. Case presentation A 52-year-old male was being investigated for having post-prandial gaseous abdominal distention. Computed tomography of the abdomen showed a heterogeneous mass lesion measuring 27 × 24 mm at the upper/mid pole of the right kidney. It also revealed two small (10 and 11 mm) benign bone islands in the body of the D4 and L4 vertebrae. The patient underwent a metastatic workup by computed tomography, which revealed a 93 × 35 mm mass in the left thyroid lobe with coarse calcification. A partial nephrectomy was planned for the renal mass, but the site of the mass deemed this impossible. Six months after the operation, the patient underwent total thyroidectomy. Histopathology of both tissue samples revealed concomitant clear cell renal cell carcinoma with heterotopic bone formation and papillary thyroid microcarcinoma. Conclusion Although rare, osseous metaplasia in renal cell carcinoma can occur and may indicate an early-stage carcinoma with a favorable prognosis.

Papillary thyroid carcinoma is the most common endocrine malignancy. Papillary thyroid microcarcinomas (PTMCs) are tumors with a size of ≤1 cm. The biological behavior of these tumors differs due to the presence of their aggressive features. The prognosis of PTMCs with high-risk features, such as clinical node metastasis, distant metastasis, and significant extrathyroidal extension to the tracheal or recurrent laryngeal nerve invasion, is poor, even if a sufficient immediate surgery is performed at diagnosis. However, PTMCs without these aggressive features are low-risk tumors because of their indolent and slow growth behaviors. The increase in thyroid cancer incidence is mostly a result of overdiagnosis of small low-risk PTMCs with indolent clinical course. Despite the sudden increase in thyroid cancer incidence worldwide, cancer mortality did not increase. Although the traditional treatment strategy for PTMC is immediate surgery at diagnosis, because of the rather low disease-specific mortality rate, low recurrence rate, and potential risk for postoperative complications, active surveillance has been proposed recently as an alternative option for PTMCs without invasion, metastasis, or cytological or molecular characteristics. The recent data support that active surveillance of low-risk PTMC should be the initial treatment modality, because only a small percentage of low-risk PTMCs show signs of progression, and delayed surgery has not caused significant recurrence. However, recent management guidelines are shifting toward more conservative treatments, such as active surveillance. Although there is an increase in the number of studies related to active surveillance, prospective studies have been mostly from academic referral centers in Japan. The world still needs class 1 evidence extended prospective studies originating from different geographic regions. Active surveillance may be a good alternative to immediate surgery for appropriately selected patients with PTMC., Competing Interests: Conflict of Interest: None declared., (Copyright: © 2018 by The Medical Bulletin of Sisli Etfal Hospital.)