Case report
A 62-year-old woman presented with complaints of a painless hoarseness and a palpable right lymph node. Laryngoscopy initially showed right recurrent nerve paralysis, and an ill-defined tumor mass was found in the right thyroid lobe using ultrasound. A computed tomography (CT) scan revealed that the tumor measured over 60 mm replacing the thyroid lobe and extended into the strap muscles compressing the trachea (Figure 1a). Multiple metastases into cervical lymph nodes and lung were also observed in the CT scan. Furthermore, after a fine needle aspiration biopsy, an anaplastic or poorly differentiated carcinoma was strongly suspected. After the diagnosis of poorly differentiated carcinoma, lenvatinib, a multi-receptor tyrosine kinase inhibitor, was used as a first-line treatment. During lenvatinib administration, a liver metastasis was detected in a CT scan that gradually progressed (Figure 1b). To prevent spontaneous intra-tumoral hemorrhage in the liver metastasis and a life-threatening tracheal invasion at the primary site, both primary and metastatic lesions were surgically resected. Postoperative pathology reported that CD5, p40, p63, and c-Kit were highly expressed, whereas TTF-1 and PAX8 expression were negative in the tumor tissue, concluding that the tumor was a metastatic ITTC (Figure 1c & 1d). The patient’s treatment strategy was switched from lenvatinib administration to scheduled hypofractionated radiotherapy (45 Gy in 15 fractions) followed by weekly paclitaxel administration. However, the patient discontinued paclitaxel treatment because of paclitaxel-induced severe side effects. After a failure of chemoradiotherapy, her liver metastasis re-emerged and rapidly progressed.
To explore more effective and optimal treatments for this metastatic ITTC, after obtaining the informed consent from the patient, we investigated the specific genetic mutation profile within the liver metastatic lesion using NGS-based cancer mutation analysis. The specific genetic mutations in metastatic ITTC were shown in Table 1. Among those mutations, focal copy number amplifications in CD274 andPDCDILG2 , which are encoding PD-L1 and PD-L2 as immune checkpoint proteins, were detected. Abundant expression of PD-L1 protein was also found on most of the tumor cells by conventional immunohistochemistry (IHC) (Figure 2), suggesting that an immune checkpoint signaling pathway is associated with tumor progression in metastatic ITTC.
We subsequently visualized the spatial distribution of PD-L1+ tumor cells and PD-1+CD3+ T cells in the metastatic ITTC using multiplex IHC. Interestingly, the number of tumor cells expressing PD-L1 was higher in the marginal area than that in the tumor nest (Figure 3a). Intra-tumoral and stromal distribution of PD-1+CD3+ T cells was also observed in the metastatic ITTC (Figure 3a). Next, we examined whether CD3+CD8+ T cells, a cytotoxic subtype of T cells, express PD-1 in metastatic ITTC by using Image cytometry and multiplex IHC. Interestingly, 41.86 % CD3+CD8+T cells expressed PD-1 on their membranes (Figure 3b and 3c). Moreover, we evaluated PD-1 expression on CD3+CD8+ T cells in the tumor nest and in the marginal and stromal areas. The number of PD-1+CD3+CD8+ T cells tended to be higher in the tumor nest and the marginal area than that in the stromal area (Figure 3d). These data indicated the existence of immunosuppression via a PD-1/PD-L1 pathway in the metastatic ITTC, and a PD-1/PD-L1 pathway could be therapeutically targeted.
Given our immune data, we made the treatment decision to administer pembrolizumab to block the PD-1/PD-L1 pathway in this case. However, the patient’s liver metastasis rapidly progressed, leading to a deterioration of her physical condition. Pembrolizumab was then no longer an option for controlling the metastatic ITTC, and the patient died because of her liver metastasis.