Three Cases of Anaplastic Thyroid Carcinoma Transformation and Leukocytosis during Lenvatinib Treatment

Since 2015, the cancer treatment lenvatinib has been used for patients with advanced radioactive iodine- (RAI-) refractory thyroid differentiated cancer; however, the drug's long-term effects have not been fully investigated. We report three cases in which lenvatinib treatment initially improved the patients' conditions, although they all died approximately 2 months after leukocytosis due to very aggressive disease progression with anaplastic thyroid carcinoma transformation. Serum interleukin-6 (IL-6) was elevated in all three cases, and granulocyte-colony stimulating factor (G-CSF) was elevated in two cases. The patients had a similar clinical course, with multiorgan metastasis and aggressive disease progression. Even with advanced cancer, lenvatinib has provided control of the disease. However, as long-term use of lenvatinib grows, it is possible that similar cases will increase, and we report our findings as an alert to other clinicians.


Introduction
Lenvatinib has been recognized to be effective against progressive radioactive iodine-(RAI-) refractory differentiated thyroid carcinoma (DTC) [1]. is targeted cancer drug has been used in Japan with documented effectiveness since 2015 [2]. We saw three patients who underwent lenvatinib treatment and died approximately 2 months after anaplastic transformation with leukocytosis. ey initially saw good results and shrinkage of their tumors from the lenvatinib use, but they developed excessive leukocytosis and rare anaplastic thyroid cancer. ere have been other cases where patients who were later diagnosed with anaplastic thyroid cancer (ATC) originally presented with excessive leukocytosis and high levels of granulocyte-colony stimulating factor (G-CSF) and interleukin-6 (IL-6) [3]. Very rarely, leukocyte hyperplasia and rapid disease progression have been reported as aggressive cancers in the lung or stomach [4,5]. In addition to describing our patients' experience with this aggressive disease, we will caution other clinicians about the possible consequences of long-term lenvatinib treatment.

Case Presentation
e following three patients were initially diagnosed with DTC and treated at the Kanagawa Cancer Center, Japan. During the postoperative follow-up, disease progression with distant metastases was observed, followed by treatment with lenvatinib. Although the treatment process was satisfactory, anaplastic transformation developed unexpectedly with leukocytosis and aggressive disease progression. is study was approved by the Institutional Review Board of Kanagawa Cancer Center (IRB approval number 27-61 for DTC and 28-49 for ATC). All patients provided a comprehensive consent stating that their samples collected for medical examination can be utilized for investigation and clinical research.
Case 1 was a 58-year-old woman with an unexceptional medical history (height: 152 cm and weight: 42 kg). She had been diagnosed with thyroid cancer that metastasized to the lungs and pelvis; she had previously undergone total thyroidectomy in 2015. e pathology was follicular thyroid carcinoma containing poorly differentiated components, and she was treated postoperatively by external beam radiation to the left pelvis, denosumab, and three courses of RAI treatment. e pelvic metastasis remained unchanged, the pulmonary metastasis was exacerbated, and her serum thyroglobulin (Tg) level gradually increased in 5 years after the initial surgery. en, we started treatment with lenvatinib at an initial dose of 14 mg, decreased to 10 mg after eight weeks, and the adverse events (AE) included grade 1 hypertension (HT) and grade 1 appetite loss. e pulmonary metastasis decreased slightly, but the pelvic metastasis remained unchanged; the efficacy according to the response evaluation criteria in solid tumors (RECIST) was stable disease [6]. Twelve weeks after commencing lenvatinib treatment, she developed a high fever with excessive leukocytosis (white blood cells (WBC) � 50300/μL).
When the lenvatinib treatment was discontinued, her WBC increased to 70,800 μL, followed by an increase in G-CSF to 748 pg/mL and IL-6 to 114 pg/mL; there was a continued progression of the pulmonary metastasis, pleural effusion, and a rapid increase in the necrosis of the left pelvic metastasis ( Figure 1). Drainage was performed, and cytology was submitted twice, but it was negative. e patient transitioned to best supportive care (BSC) and died 51 days later. e duration of lenvatinib treatment was 5.1 months.
Case 2 was a 70-year-old woman with an unexceptional medical history (height: 157 cm and weight: 50 kg). She had surgery in 2004 previously for papillary thyroid carcinoma (PTC), and multiple pulmonary metastases were recognized in 2009. RAI treatment was performed twice but was ineffective for the pulmonary metastasis, which gradually increased. Active surveillance continued with thyroid stimulating hormone (TSH) suppression therapy, but the pulmonary tumor increased to 17 mm in 2015. We started lenvatinib treatment at the initial dose of 24 mg, which was reduced to 10 mg after 12 weeks. e AE induced by lenvatinib included grade 3 HT, grade 1 alopecia, and grade 2 arthralgia. e tumor shrank upon treatment, from 17 to 9 mm in diameter, and the RECIST efficacy was categorized as a partial response. While the disease condition was stable for 56 months following lenvatinib treatment, her WBC unexpectedly increased to 19,700, and a computed tomography (CT) scan showed exacerbation of the pulmonary metastasis, left lung S3 atelectasis, and pleural effusion, which gave a negative cytology result; she was reclassified with progressive disease. Her WBC continued to increase to 33,700, G-CSF was 22.4 pg/mL, within a normal range, but IL-6 was  elevated to 22.8 pg/mL. When her physical condition began to deteriorate, with weight loss and an inability to walk, a CT scan revealed multiple metastases on the liver, left adrenal gland, and kidneys ( Figure 2). She transitioned to BSC and died 50 days after the rise in WBC. e duration of lenvatinib treatment was 5.09 years. Case 3 was a 71-year-old woman with a history of HT, hyperlipidemia, and chronic kidney disease (height: 154 cm and weight: 73 kg). She was diagnosed with PTC, and her initial surgery was performed in 2002. Multiple pulmonary metastases had been recognized in 2011, but RAI treatment was not effective. e maximum diameter of pulmonary metastasis was 6 mm, the serum Tg level remained stable at <1 ng/dL for 8 years after the diagnosis of pulmonary metastasis, and active surveillance was continued with TSH suppression; however, the size of the pulmonary tumor increased to 15 mm in 2019.
We started lenvatinib treatment at the initial dose of 14 mg, which was reduced to 10 mg after four weeks. e AE induced by lenvatinib included grade 2 HT and grade 1 stomatitis. e tumor shrank from 15 mm to 6 mm in diameter, and the efficacy was categorized as a partial response. Ten months after commencing lenvatinib treatment, her WBC increased to 19,700, and a CT scan showed multiple new lesions of 28 mm, changing her disease category to progressive disease (Figure 3). Her WBC increased to 33,700, G-CSF to 617 pg/mL, and IL-6 to 46.4 pg/mL. She developed low back pain, and an examination revealed progressive pulmonary and pelvic bone metastases. She was given 20 Gy external beam radiation to treat bone metastasis but suffered weight loss. She transitioned to BSC, and she died 66 days after the initial rise in WBC. e duration of lenvatinib treatment was 13.5 months.

Characteristics of Anaplastic
yroid Carcinoma Transformation. ATC is one of the most aggressive neoplasms. ere have been several reports of leukocytosis due to the leukemoid paraneoplastic reaction resulting from G-CSF, granulocyte-macrophage (GM) CSF, and IL-6 production. Excessive WBC counts that continue to increase are linked to a poorer prognosis [7][8][9][10][11]. However, there are very few reports where leukocytosis is a primary marker in an ATC diagnosis. Since 1992, 17 cases diagnosed as ATC with leukocytosis have been reported worldwide, of which 13 cases have been in Japan [3]. It is significant that three patients in the same facility were diagnosed within 3 months for this disease. e clinical course of each case was similar, and it is especially notable that each treatment course was controlled by the use of lenvatinib.

Blood
Results. Table 1 shows inflammatory reactions demonstrated by increased WBCs, hemoglobin, platelet counts, neutrophil-lymphocyte ratio, C-reactive protein (CRP), G-CSF, and IL-6 in all cases. Figure 4 shows the WBC counts, which remained high in all patients, although the CRP did not decrease. e high fever observed in cases 1 and 2 was successfully treated with naproxen, but the leukocytosis did not subside. Lenvatinib was continued. After the WBC increased, the disease progressed rapidly, and all of them died approximately 2 months later. e serum Tg levels for each patient are shown in Figures 1-3, but Tg levels cannot be used as an indicator in ATC; so, the disease progression and the increase in Tg were not linked.

Analysis of G-CSF and IL-6 and
Cancer. G-CSF is a growth factor that is known to be a key regulator of hemopoiesis and for the proliferation and differentiation of neutrophils. G-CSF-producing tumors have aggressive characteristics that have been the subject of many Japanese investigations [4,5,12]. G-CSF-producing malignant tumors are sometimes accompanied by fever and high CRP levels, but G-CSF itself does not have the effect of inducing  these reactions, and an inflammatory cytokine such as IL-6 could be involved. IL-6 is secreted by T lymphocytes; it differentiates B lymphocytes into antibody-producing cells and is an acute phase response during inflammation [13].

Future Monitoring and Investigation.
In the future, if a patient experiences progressive disease while being treated with lenvatinib, the clinician should investigate whether anaplastic transformation has developed. Since there are limited long-term results for lenvatinib treatment alone, genetic tests should be performed, and if indicated, BRAF inhibitors and PD-L1 inhibitors should be used in combination; however, these are not yet available for clinical use in Japan [14]. Until then, clinicians should monitor the clinical course and leukocyte levels of patients being treated with lenvatinib. e findings from our institution also warrant further research from other investigators whose patients have had a similar clinical course.
Data Availability e datasets used and/or analyzed during the current study are available from the corresponding author upon request.

Conflicts of Interest
e authors declare that they have no conflicts of interest. Case Reports in Endocrinology 5