Tumor-to-Tumor Metastasis of Renal Cell Carcinoma to a Follicular Variant of Papillary Thyroid Carcinoma: A Case Report and Literature Review

Abstract

Renal cell carcinoma (RCC) is the most common renal malignancy. It has a variable clinical course with metastasis to unusual sites occurring months to years after the initial diagnosis. However, metastasis can also be the first presentation of RCC. Although relatively uncommon, the thyroid gland is the most common location for RCC metastasis in the head and neck region. Tumor-to-tumor metastasis is an exceedingly rare occurrence. Only 10 cases were reported of RCC metastasis to primary thyroid neoplasms. We present a case of clear cell RCC metastasizing to a follicular of variant papillary thyroid carcinoma (FVPTC) 14 years after the initial diagnosis of RCC. A review of similar reported cases revealed that the most common primary thyroid recipient of tumor-to-tumor metastasis of RCC was FVPTC. The rich lymphovascular network in FVPTC compared to other thyroid tumors, which may promote the deposition of metastatic tumor cells, might explain this predilection. Careful review of the clinical and radiological findings and checking for any history of malignancy when examining thyroid nodules is important for guiding further studies. Performing a targeted panel of immunohistochemical stains for any suspicious areas is also essential for the diagnosis of such unusual cases.

Tumor-to-Tumor Spread: A Case Report and Literature Review of Renal Cell Carcinoma Metastasis into Thyroid Cancer

“…Renal cell carcinoma represents 90% of all renal tumors and 3% of adult malignancies (3). The classic ndings of ank pain, hematuria and a palpable mass are only present in 10% of patients and most are diagnosed after incidental imaging ndings (4).…”

“…in 1968 that includes: two or more distinct tumors, with the recipient being a true neoplasm, and a true metastatic deposit within the neoplastic tissue of the recipient tumor. Furthermore, this de nition excludes collision tumors, lymphovascular spread without actual invasion and metastasis into hematopoietic malignancies (3,25). Interestingly, RCC can act as both a donor and recipient.…”

“…When one is viewed inside the other, as seen in RCC metastasizing to the thyroid, pathologists are faced with a quandary (7). Another feature that can be relied on for proper diagnosis is a multifocal growth pattern and sinusoidal patterns of vascularity (3,17). Close attention should be paid to intraluminal erythrocytes, or so-called "bloody follicles" which are suggestive of metastatic RCC (5).…”

“…Primary thyroid tumors stain positive for thyroglobulin (TG) and thyroid transcription factor-1 (TTF-1). On the contrary, clear cell RCC stains positive for a variety of markers such as vimentin, galectin-3, CD10, CAIX, renal cell carcinoma (RCC), PAX-8 and epithelial membrane antigen (EMA) (3,17). However, caution should be taken with the use of PAX-8 because it can be expressed in both thyroid and renal neoplasms as well as other tumors gynecologic origin.…”

Prostate Adenocarcinoma Within a Thymoma: A Rare Case of Tumor-to-Tumor Metastasis

“…To date, more than 100 TTM cases were published in the literature and lung cancers are the most common donors in TTM, followed by carcinomas of the breast, gastrointestinal tract, prostate, and thyroid. The most frequent recipient tumor is renal cell carcinoma, followed by meningioma and thyroid tumor [2][3][4][5]. Thymoma is considered a rare neoplasm with an overall incidence of 1.5 cases per million whereas the incidence of thymic malignancies is 0.13 cases/100.000 persons/year [6].…”