Morphological examination
Grossing, a piece of gray-red tissue 5×3×2 cm in volume was removed from the left thyroid. The section showed a mass of 2.5 cm in diameter, gray-white colors, and hard in texture. The resected right thyroid gland was 4×2.5×2 cm in volume, with grayish red colors, nodular shape, and medium texture. Besides, more than 20 lymph nodes in the central region of the left neck and 6-8 cervical regions were examined. The lymph nodes are enlarged, ranging from 0.5 to 3 centimeters in diameter. Histologically, on the left side of the thyroid, H&E slides showed hyperplasia of thyroid follicular epithelial under the background of HT(figure 1-A), and the follicular epithelium in the focal area of HT was transformed into PTC(figure 1-B). Importantly, in addition to a typical subtype of PTC(figure 1-C), there were other subtypes of PTC, such as oncocytic variant(figure 1-D), follicular and solid patterns(figure 1-E). In some focal areas, we also found metaplasia of columnar epithelium into squamous epithelium(figure 1-F).
Immunohistochemistry staining (IHC)
To further clarify the nature and types of the tumor, we performed immunohistochemistry staining (IHC) on a series of antibodies, including CK19, TPO, TG, CD56, TTF-1, Galectin-3, etc. on formalin-fixed paraffin-embedded (FFPE) tissues. A list of all antibodies is shown in table 1. IHC staining indicated that it was a typical pattern of PTC in which CK19, TTF1, and Galectin-3 were strong positive, and TPO, CD56, and TG were negative showed in figure 2(A-F). IHC also showed that CT, MC, and Syn were negative (not showed).
Imaging and surgical findings
After the first operation, the patient took levothyroxin sodium tables 100ug/day regularly. Fourteen months later, the patient herself found a mass in the anterior region of the left neck, which was gradually enlarged, and the left upper limb occasionally felt numbness and pain, and then came to our hospital for a medical treatment. Physical examination: A mass was palpable in the anterior region of the left neck, about 8 cm in maximum diameter, texture hard, unclear boundary, and poor mobility. Contrast-enhanced CT scanning in the neck diagnosed that the thyroid gland in both sides was absent, and the mass in the left neck supraclavicular region was considered as PCT postoperative recurrence or lymph nodes metastasis (figure 3-A). Systemic PET/CT examination: PET/CT showed that the bilateral lobe of the thyroid was absent after operation, and there was no definite sign of a malignant tumor in the operation area. The tumor in the IV-V area of the left neck showed internal necrosis and increased glucose metabolism in a ring. There were several lymph node metastases showed in the left neck (II-V) region showed in figure 3-B.
After multidisciplinary discussion in our hospital, it was considered that there was a symptom of tumor compression, and due to the effect of radiotherapy and chemotherapy was not obvious, so we choose the operation to reduce the burden of the tumor. It was found during the operation that the boundary among the original operating area and sternocleidomastoid muscle, and local cervical skin was not clear. The space between the lesion and the common carotid artery was disappeared, the trachea was compressed to the right, and the left internal jugular vein was not seen (showed in figure 3-C). Multiple lymph nodes were removed in the left neck II-V regions, it was possible to consider lymph nodes metastasis (showed in figure 3-D).
Pathological examination of local lymph nodes
Postoperative pathology confirmed that it was metastatic carcinoma of lymph nodes. Interestingly, there were various types of carcinoma in metastatic lesions, including classical papillary carcinoma(figure4-A), tall columnar papillary carcinoma(figure4-B), SCC(figure4-C), and undifferentiated cell carcinoma or thyroid anaplastic cancer (figure4-D). In order to further clarify the characteristics of these tumor cells, we performed IHC on these tumor cells. There was a patchy nesting area of poorly differentiated or undifferentiated carcinoma in local lymph node metastases(figure5-A). The IHC results showed that the tumor cells had the dual characteristics of PTC and SCC, which P40, P63, CK5/6,TTF-1, and CK19 were strongly positive showed in figures 5B-F. These results strongly suggested that the tumor had double characteristics of PTC and SCC.
A comparative study of IHC and molecular pathology in primary PTC and SCC within local lymph node metastasis
For further exploring the biological and origin relationship between primary PTC and SCC in local lymph node metastasis, we made a comparative study by IHC and molecular pathology. Firstly, we compared the expression of PD-L1, TP53, BRAFV600E, and Ki67 in primary thyroid tumor and local lymph node metastasis by IHC. The results indicated that PD-L1 is negative in the primary tumor (figure 6-A) and a strong positive in metastatic tumors (figure 6-E). TP53 was expressed in both primary and metastatic tumors, but the positive rate in tumor cells was different. The expression rate of TP53 in primary tumors is about 20% (figure 6-B), while in metastatic tumors, the expression rate of TP53 is about 80% (figure 6-F). BRAFV600E was expressed in both primary and metastatic tumors, and there was no significant difference in the positive rate (figure 6-C and G). In primary tumors, the Ki67 proliferation index is about 5% (figure 6-D), while in metastatic tumors, the Ki67 proliferation index is about 30% (figure 6-H). Then, we detected the mutations of BRAF exon 15, KRAS exon 2-4, NRAS exon 2-4, HRAS exon 3, PIK3CA exon 20, and TERT promoter mutation in primary and metastatic tumors by QPCR to further clarify the relationship between them. The results showed that BRAF exon 15 mutation was found in both primary and metastatic tumors, and no other gene mutations were found (figure 7A-B).
Further treatment and follow-up
After the second operation, she received radiotherapy for two months. The effect of radiotherapy was not good, and the patient finally gave up the treatment, which is still under follow-up.