Metastasis of colon cancer to the thyroid and cervical lymph nodes: a case report
Discussion
Metastases to the thyroid gland are uncommon. The incidence of thyroid metastasis among colorectal cancer patients is quite low: this diagnosis is applied to 6 patients (0.1 %) out of a total of 5862 colorectal cancer patients [1]. Recently, Chung et al. [2] reviewed all clinical reports available in the literature from 2000 to 2010 including case reports and case series. In this analysis of thyroid metastases, primary cancers were identified as renal (48.0 % of cases), colorectal (10.4 %), lung (8.3 %), breast (7.8 %), or sarcoma (4.0 %).
While 60 to 80 % of metastases are metachronous (following previously treated malignancy), 20 to 40 % are synchronous (simultaneous) with the primary lesion [3]. In metachronous metastases, the mean and median intervals between diagnosing primary malignancies and their metastases to the thyroid gland were reported at 69.9 and 53 months, respectively [2]. The mean interval between discovery of primary tumor and of thyroid metastasis was 68 months for renal cancer, 48.2 months for breast cancer, 41.5 months for colorectal cancer, and 20.9 months for malignant melanoma. Another report indicated a very poor prognosis for thyroid metastasis from colorectal cancer: a cancer-related death rate of 50 % in less than a year [3]. For such cases, systemic management depending on the primary colon cancer may contribute to longer survival following thyroid surgery.
Froylich et al. [4] reviewed metachronous colon metastasis to the thyroid. The authors found 34 cases; two thirds of the patients were female and patient age ranged from 34 to 85. The metastases’ primary sites were the rectum (41 %), sigmoid colon (33 %), right colon (19 %), or left colon (11 %). The staging of the colon carcinoma was stage III or IV in 75 % of the patients. Metastasis to the thyroid was diagnosed 6 months to 8 years after colonic resection. In our case, the staging of the sigmoid colon cancer was stage II. The thyroid metastasis was revealed at 5 years after sigmoid colon cancer surgery.
Although a high sensitivity has been reported for FNA in patients with various metastatic carcinomas to the thyroid gland, the accuracy of FNA is around 50 % [5, 6]. IHC is usually able to differentiate between primary thyroid malignancy and secondary malignancy [7, 8]. In general, thyroid tumor test results are positive for CK7 and negative for CK20. In contrast, colon cancer results are almost always positive for CK20 and negative for CK7. In our case, the tumor cell results were positive for CK20 and negative for CK7.
The role of surgery for treating thyroid metastasis is unclear. Thyroidectomy constitutes better palliation of respiratory symptoms than mere observation [9]. Local control of metastatic disease in the central compartment of the neck can be successfully achieved with minimal morbidity with surgical resection in selected patients [5]. Nonsurgical treatments, such as radiotherapy and chemotherapy, have been used for patients deemed inoperable, although the impact of these modalities remains uncertain [10]. Although our patient had recurrent laryngeal nerve palsy, surgery appeared to give her relief and prevention from local symptoms.