a secondary neoplasm of the thyroid gland is a distinctly uncommon cause of thyroid enlargement , the reported prevalence of which range from 2% to 3% of all thyroid malignancies , autopsy series , however , report a prevalence varying from 1.25% to 24% these tumors mimic primary thyroid gland tumors and often lead to diagnostic difficulties .
herein , we report an interesting case of secondary thyroid cancer coexisting with a micropapillary carcinoma in a 67-year - old male patient following a left radical nephrectomy done 15 years prior for a fuhrman grade iii pt3n0m0 renal cell carcinoma ( rcc ) . we additionally discuss the issues and challenges in its diagnosis and the role of palliative thyroidectomy in metastatic rcc with a thyroid gland secondary .
a 67-year - old man with no comorbid conditions presented to us with the complaints of swelling in the anterior neck of 3 months duration .
a rapid increase in size of the swelling and with associated pain and difficulty in breathing for a couple of weeks prompted him to seek medical attention .
he had undergone a left radical nephrectomy done 15 years prior at our center for a fuhrman grade iii pt3n0m0 rcc following which he defaulted .
physical examination revealed a well - circumscribed firm to hard swelling arising from the right lobe of the thyroid gland measuring 8 cm  8 cm , which was pushing the trachea to the left of the midline .
fine needle aspiration cytology ( fnac ) from the thyroid swelling suggested a poorly differentiated carcinoma with a possibility of metastasis from a renal primary . a subsequent tru - cut biopsy with immunohistochemistry ( ihc )
correlation ( immunopositivity to vimentin , epithelial membrane antigen , ki-67 and cd10 positive and negative for thyroglobulin , thyroid transcription factor-1 , and calcitonin ) revealed a tumor with clear cell histology confirming a diagnosis of metastasis from a rcc [ figure 1a - d ] .
( a ) positron emission tomography ( pet)-computed tomography showing an ill - defined heterogeneous mass with a large necrotic component and increased metabolic activity in the right lobe of thyroid standardized uptake value ( suv - 7.2 ) which was causing mass effect over right neck great vessels and trachea .
( b ) pet avidity in the nodule in left lower lobe lung ( suv - 1.7 ) a positron emission tomography ( pet)-computed tomography done for metastatic workup revealed an ill - defined heterogeneous mass with a large necrotic component and increased metabolic activity in the right lobe of thyroid standardized uptake value ( suv - 7.2 ) , which was causing mass effect over right neck great vessels and trachea [ figure 1a and b ] . in addition , pet avidity was noted nodule in left lower lobe lung , ( suv - 1.7 ) , multiple mediastinal nodes , ( suv - 1.7 - 2.2 right adrenal soft tissue lesion ( suv - 4.6 ) , and multiple nodules ( suv - 3.2 ) along the body and tail of the pancreas [ figure 2a and b ] .
( a and b ) positron emission tomography - computed tomography scan showing right adrenal soft tissue lesion standardized uptake value ( suv - 4.6 ) and multiple nodules along the body and tail of the pancreas ( suv - 3.2 ) a palliative total thyroidectomy [ figure 3a and b ] was contemplated in view of the compressive and obstructive symptoms , the final histopathology of which revealed an 8 cm  7 cm  4.5 cm tumor replacing entire right lobe of the thyroid , which on microscopy revealed a neoplasm arranged as nests of cells with round to oval nuclei , clear cytoplasm , and fibro - vascular septa .
the thyroid follicles were compressed at periphery , capsular infiltration , and occasional vascular tumor emboli were also noted .
the final diagnosis confirmed the preoperative diagnosis of metastatic rcc , clear cell type , fuhrmann grade iii , with an additional focus of papillary micro carcinoma in the left lobe of the thyroid [ figures 4a - d , 5a - d ] .
the patient made an uneventful recovery and was subsequently started on targeted therapy ( tablet sunitinib 50 mg orally once a day ) and continues to be on follow - up for 4 months , relieved of his compressive symptoms .
( a ) clinical photograph showing the 8 cm  8 cm swelling arising from the right lobe of thyroid ( b ) clinical specimen photograph following palliative total thyroidectomy ( a and b ) microscopy examination of the thyroidectomy specimen revealed a neoplasm arranged as nests of cells with round to oval nuclei , clear cytoplasm , and fibro - vascular septa .
the thyroid follicles were compressed at periphery , capsular infiltration ( h and e , 20 ) ( c ) vascular tumor emboli ( h and e , 10 ) .
( d ) an additional focus of papillary micro carcinoma in the left lobe of the thyroid ( h and e , 10 ) ( a ) tumor cells showing immunopositivity to vimentin , immunohistochemistry ( ihc , 10 ) ( b ) tumor cells with immunopositivity to cd10 ( ihc , 10 ) ( c ) tumor cells with immunopositivity to epithelial membrane antigen ( ihc , 10 ) ( d ) tumor cells with immunopositivity to ki-67 ( ihc , 10 )
the vast majority of the malignant tumors that involve the thyroid gland are primary tumors which include papillary , follicular , medullary , and anaplastic carcinomas .
. primary tumors of the kidney ( 48.1% ) , colorectal ( 10.4% ) , lung ( 8.3% ) breast ( 7.8% ) , and sarcoma ( 4.0% ) are the most common tumors reported to metastasize to the thyroid .
it has been widely believed that the thyroid gland , because of its abundant vascular supply is a vulnerable site for metastatic involvement .
a few authors have additionally proposed that the susceptibility of the thyroid gland to metastatic growth is increased when affected by goiter , neoplasms , or thyroiditis , and this can be explained due to metabolic changes in the thyroid gland , some other authors have , however , refuted this claim .
metastasis from rccs has been reported to account for nearly 12 - 34% of all secondary thyroid tumors .
these tumors may represent the first manifestation or may present as a synchronous or metachronous metastasis in a preexisting clear cell renal carcinoma .
the metastases usually are reported to appear as metachronous lesions , often several years after nephrectomy .
although metastasis to the thyroid gland should be suspected in patients with a history of renal tumors , a definitive preoperative diagnosis of primary versus a secondary tumor may not always be straightforward .
an fnac of thyroid gland is useful in the diagnosis of secondary tumors as well .
the differential diagnosis for tumors with clear cell appearance should include paragangliomas , differentiated thyroid cancer , lung , and salivary gland secondary tumors .
a background knowledge of the primary tumor would aid the pathologist in choosing the appropriate ihc markers for confirmation of the final diagnosis , as was used in our patient .
there are no clear guidelines regarding the role of thyroidectomy in secondary thyroid tumors from rccs since most clinical studies have included a small numbers of patients .
a hemi or a total thyroidectomy is generally recommended in patients with no other metastases ; wherein the long term prognosis is good .
a palliative thyroidectomy is usually reserved for patients with disseminated disease only in the presence of compressive symptoms as was successfully done in our patient .
interestingly , the previously described association of thyroid and pancreatic metastases of rcc was also noted in our patient . the management of metastatic rccs has undergone dramatic changes over the last decade , and this has mostly been due to the introduction of many targeted agents which have had a positive impact on the overall survival .
the role of metastasectomy in the era of targeted therapy is evolving and needs to be better elucidated .
the possibility of metastatic rcc should be kept as a differential during the course of the evaluation of clear cell tumor of the thyroid gland , more so when found in a patient with a prior history of renal tumor , irrespective of the duration .
the coincidental association of thyroid and pancreatic metastases in rcc needs to be further explored .
metastatectomy has the potential to improve the quality of life and possibly survival in a selected group of patients and should be judiciously used in patients with secondary thyroid tumors from an rcc .
 a secondary neoplasm of the thyroid gland is a distinctly uncommon cause of thyroid enlargement . 
 these tumors mimic primary thyroid gland tumors and often lead to diagnostic difficulties . 
 we report an interesting case of secondary thyroid tumor coexisting with a micropapillary carcinoma in an elderly male patient following a radical nephrectomy done 15 years prior for a renal cell carcinoma ( rcc ) . 
 interestingly , the previously described coincidental association of thyroid and pancreatic metastases in a metastatic rcc was also noted in our patient as was demonstrated in the positron emission tomography - computed tomography which was done as part of the metastatic workup . 
 this association needs to be further explored as also the role of palliative thyroidectomy in the setting of a metastatic rcc . 
 the possibility of metastatic rcc should be kept as a differential during the course of the evaluation of clear cell renal tumor of the thyroid gland . 