Tumors of the neck showing thymic or related branchial pouch differentiation: a unifying concept

Intrathyroidal Thymoma: A Diagnostic Challenge

Intrathyroidal thymoma is a rare tumor that can be challenging to diagnose due to its unusual location and resemblance to more common thyroid conditions. We present the case of a 58-year-old woman with an incidentally discovered thyroid nodule during evaluation for an upper respiratory infection. Ultrasonography revealed an exophytic nodule in the left thyroid lobe, categorized as TR 3. Fine-needle aspiration cytology suggested a neoplastic process, leading to a left hemithyroidectomy. Histopathology confirmed a diagnosis of intrathyroidal thymoma, Type B2, with extensive necrosis, and immunohistochemistry validated the findings. This case underscores the diagnostic challenges of intrathyroidal thymoma, emphasizing its consideration in the differential diagnosis of atypical thyroid nodules. Despite the difficulties in preoperative identification, surgical resection and subsequent histopathological examination remain essential for a definitive diagnosis. The patient is currently under surveillance, and there is no evidence of residual thymic tissue or abnormalities in the remaining thyroid tissue.

Spindle epithelial tumor with thymus-like elements (SETTLE): a diagnostic challenge with distinct therapeutic implication; case report

Spindle epithelial tumor with thymus-like elements (SETTLE) is a rare malignant neoplasm of the thyroid gland which is believed to arise from intrathyroidal thymic tissue. It predominantly affects young adults and children presenting with a thyroid mass of variable duration and rarely occurs in adults. It has a high overall survival with a tendency for delayed metastasis. SETTLE is a biphasic lobulated tumor composed of spindle shaped cells along with glandular formations seen on histopathological examination. Despite its typical morphology it is commonly misdiagnosed on histopathology due to its rarity and overlapping morphology with other close mimics such as a carcinoma, synovial sarcoma and thymoma. Herein we report such a case occurring in a middle aged female presenting with a neck mass. She had an initial diagnosis of metastatic poorly differentiated squamous cell carcinoma possibly with an orophayngeal primary in view of co expression of CK, p40 and p16 on immunohistochemistry. The patient underwent surgical resection with modified neck dissection. On review at our hospital it was diagnosed as SETTLE and she remains disease free after a follow-up period of 1 year. Diligent histopathological examination espoused with a judicious panel of IHC markers in conjunction with clinicoradiological findings forms the mainstay of diagnosis. Diffuse and strong p16 immunoexpression has not been documented or evaluated in literature so far, and needs to be explored for its diagnostic utility in this rare entity.

Spindle epithelial tumor with thymus-like element (SETTLE)-Report of a rare thyroid carcinoma

Spindle epithelial tumor with thymus-like element should be included in the differential diagnosis of thyroid gland cancers, particularly in medullary carcinoma, younger patients and indolent clinical presentation, because it may influence treatment and prognosis.

Carcinoma Showing Thymus-like Differentiation (CASTLE) with Synchronous Papillary Thyroid Carcinoma: A Case Report and Review

Carcinoma showing thymus-like differentiation (CASTLE) is a rare malignant tumor that accounts for 0.1%-0.15% of all thyroid cancers. More than half of the patients have tumor extension to adjacent organs, including the recurrent laryngeal nerve, trachea, and esophagus. The diagnosis of CASTLE is based on histology and immunohistochemistry. A 58-year-old female patient complained of hoarseness for one and half years. Right side vocal cord palsy was diagnosed by fiberscopy. Thyroid sonography revealed right thyroid tumors, which were reported to be papillary thyroid carcinoma through FNAC. Total thyroidectomy with central lymph node dissection was performed. Pathologist found 2 isolated malignancy tumors. One patient in the right thyroid lobe had papillary thyroid carcinoma features. The other extrathyroid tumor seemed to be separated from the first tumor and invaded the thyroid capsule. After multiple immunohistochemical studies, PTC synchronous CASTLE was the final diagnosis. Coexisting PTC and CASTLE is very rare. This is the first report to describe a case showing PTC at first, while subsequent pathologic examination revealed the presence of CASTLE in addition to PTC. Since the prognosis of CASTLE is favorable, the treatment is different from other aggressive thyroid cancers, such as poorly differentiated or anaplastic thyroid carcinoma.

Coexistence of intrathyroid thymic carcinoma and papillary thyroid carcinoma: a case report and literature review

Background

Intrathyroid thymic carcinoma (ITTC) is a rare neoplasm of the thyroid, which accounts for less than 0.15% of all thyroid malignancies. The coexistence of ITTC and papillary thyroid carcinoma (PTC) is an extremely rare condition reported only in a limited number of cases.

Case summary

A 26-year-old female presented with a growing neck mass, hoarseness, and dysphagia over four months. Ultrasonography revealed that the entire left lobe and the isthmus of the thyroid were replaced with a hypoechoic mass. Moreover, it revealed two hypoechoic nodules in the right thyroid. The patient underwent a total thyroidectomy and paratracheal lymph node dissection. Histopathological examinations revealed the coexistence of ITTC and PTC in the same thyroid. In immunohistochemical analyses, the ITTC was positive for CD5, P63, CD117, and CK 5/6 and negative for thyroglobulin, calcitonin, and TTF 1. At the same time, PTC was positive for TTF 1 and thyroglobulin and negative for CD5, P63, and CK 5/6. The patient received postoperative radiotherapy and remained well with no evidence of recurrence during one month follow-up.

Conclusion

Distinguishing ITTC from other thyroid malignancies before the surgery is challenging due to its non-specific presentations. Therefore, the diagnosis relies on postoperative studies, especially immunohistochemistry. The recommended treatment approach to improve survival in ITTC cases is total thyroidectomy combined with cervical lymph node dissection, followed by postoperative radiotherapy. The coexistence of ITTC and PTC may indicate the similarity in the underlying mechanisms of these tumors. However, further investigations are needed to understand this potential correlation.

When to settle for SETTLE! A lesson learned from our cases

Spindle epithelial tumor with thymic like elements (SETTLE) is a biphasic tumor composed of epithelial and spindle cell components. It is an uncommon indolent tumor arising in the thyroid gland and most commonly affects the children and young adults. This entity is mostly overlooked because of its rarity and diagnostic difficulty on morphology. We discuss two cases of SETTLE with varied presentation, diagnostic challenges and lessons learnt from them.SETTLE should be considered as a differential especially when dealing with a thyroid lesion in young and adolescent. The article discusses the histologic details and common mimickers to be borne in mind aiding in arrival at the final diagnosis on biopsy specimens.

Intrathyroid thymic carcinoma: A clinicopathological analysis of 22 cases

OBJECTIVE

Intrathyroid thymic carcinoma (ITTC) is a rare malignancy. The current understanding of ITTC is inadequate, and there is no standard treatment for ITTC. In the present study, we aimed to explore the clinicopathological characteristics of ITTC and identify potential therapeutic targets.

METHODS

The clinicopathological characteristics of 22 ITTC patients at our institution were reviewed. The expression of DNA mismatch repair (MMR) proteins and PD-L1 in ITTC were assessed by immunohistochemistry (IHC).

RESULTS

All patients underwent surgery. There were nine females and 13 males, with a slight male predominance. Their ages ranged from 42 to 79 years (average, 54. 1 years). The diameters of the neck masses ranged from 10 to 100 mm (average, 39 mm). Ipsilateral lymph node (LN) dissection was performed in 18 patients: 12 demonstrated LN metastasis, six showed no LN metastasis, and no lymph nodes were dissected in four. One patient had liver metastasis. CK5/6, P63, CD5, and CD117 were expressed in all cases. All cases were negative for TTF1, PAX8, thyroglobulin, and BRAF V600E. DNA MMR protein expression was retained in all tested tumors, and EBV-encoded small RNA (EBER) in situ hybridization was consistently negative. The Ki67 proliferation index ranged from 10 to 70 %. All patients were followed-up for 14-134 months, four died, six were lost to follow-up, and the remaining patients survived without disease. The PD-L1 combined positive score ranged from 10 to 80 (average: 40).

CONCLUSION

Our results confirm that CD5 and CD117 co-expression support a diagnosis of ITTC. All tumors in this cohort were DNA MMR-proficient and were not associated with Epstein-Barr virus (EBV) infection. A high CPS for PD-L1 suggests that immune checkpoint inhibitor therapy may be worthy of further exploration in patients with ITTC.

TOETVA: a single surgeon's learning curve and a case report of CASTLE thyroid tumor

BACKGROUND

Owing to the lack of visible scars, the transoral endoscopic thyroidectomy vestibular approach (TOETVA) offers superior aesthetic outcomes compared to conventional thyroidectomy. Carcinoma showing thymus-like differentiation (CASTLE) represents a rare thyroid gland neoplasm. This study aimed to explore the TOETVA learning curve and present a case report of CASTLE.

METHODS

A study with precise 1:1 matching was conducted to assess the procedure safety and cancer control outcomes of TOETVA in comparison to conventional surgery between May 2020 and May 2023. Cumulative sum analysis was employed to optimally fit the learning curve. Subsequently, a case report of CASTLE treated with TOETVA surgery was presented.

RESULTS

The mean operative time was longer in the TOETVA group than in the open group. The TOETVA group had a higher incidence of skin numbness and excellent cosmetic outcomes compared to the open group. The learning curves for work area preparation, unilateral thyroid lobectomy, and the entire surgical process were 59, 28, and 50 cases, respectively. There were no differences between the learning and proficient groups, except for operative time, intraoperative blood loss, and drainage volume on the first postoperative day.

CONCLUSIONS

A comprehensive analysis of the TOETVA learning curve utilizing cumulative and analytical methods demonstrated the feasibility of TOETVA with regards to surgical integrity, safety, and oncological safety. This study's findings suggest that a surgeon's cumulative number of TOETVA cases exceeding 50 can reach the mastery stage. Moreover, diagnosing CASTLE is challenging and necessitates immunohistochemical detection of relatively specific markers associated with thymic epithelial tumors.

Case Reports: A role of postoperative radiation therapy in completely resected early stage intrathyroid thymic carcinoma: a case report and literature review of the diagnosis and treatment

Background

Intrathyroid thymic carcinoma (ITTC) is a rare malignant tumor of the thyroid, probably arising from ectopic thymus or branchial pouch remnants. Most of the literature recommended radical resection as the fundamental treatment for ITTC, and postoperative radiation appears to be able to reduce the recurrence rate in patients with advanced ITTC. However, the issue of adjuvant radiotherapy in completely resected early-stage ITTC has been controversial.

Case presentation

Here, we reported a new case of early-stage ITTC that treated with total thyroidectomy and the right central neck dissection. Postoperative external beam radiation therapy (50.0 Gy/25 fractions) was given to the thyroid bed and bilateral cervical lymph node area since the tumor involved part of the sternal thyroid muscle. At 4-year follow-up after completion of radiotherapy, she is without evidence of locally recurrent or distant disease.

Conclusion

Since there are no current guidelines for early-stage ITTC, in combination with this case and previous literature, we may suggest routine adjuvant radiotherapy should be considered in patients with incompletely resected tumors and extraparenchymal extension of ITTC. Moreover, we summarized comprehensive and advanced diagnosis, treatment, prognosis of ITTC and comparison between ITTC, primary squamous cell carcinoma of thyroid gland, differentiated thyroid cancer, and anaplastic thyroid cancer.

Two cases of concurrent carcinoma showing thymus-like differentiation (CASTLE) coexisting with papillary thyroid carcinoma

Carcinoma showing thymus-like differentiation (CASTLE), which emerges within the thyroid gland or the adjacent soft tissues of the neck, is a rare malignant neoplasm found globally. The occurrence of CASTLE in conjunction with papillary thyroid carcinoma is an even more infrequent phenomenon. The ensuing sections elaborate upon the clinical attributes characteristic of CASTLE.

Intrathyroidal Thymic Carcinoma: A Retrospective Case Series Study

OBJECTIVE

Intrathyroidal thymic carcinoma (ITC) is a rare low-grade malignant thyroid tumor. There is neither sufficient understanding of this tumor nor its clinical treatment. This study is to explore the clinicopathological features, treatment, and prognosis of ITC and thereby provide a reference for the diagnosis and treatment of the disease.

METHODS

The clinical, pathological, therapeutic, and prognostic data of 13 patients with ITC were retrospectively analyzed.

RESULTS

The case series comprised 7 males and 6 females, with an average age of 51.9 ± 10.1 years. After surgical resection, all patients received post-operative neck radiotherapy at dosages of 60-66 Gy. Five patients with level VI lymph node metastasis additionally received 6 courses of cisplatin chemotherapy. All patients were followed-up for 21-132 months (median = 66 months), and all of them survived without recurrence or metastasis.

CONCLUSIONS

The diagnosis of ITC depends mainly on pathological and immunohistochemical results, particularly CD5 positive staining. Surgical resection is the preferred primary treatment modality which can be supplemented with radiotherapy and chemotherapy to reduce the risk of recurrence and metastasis.

Spindle Epithelial Tumor With Thymus-Like Differentiation of Thyroid (SETTLE): A Case Report and Literature Review

Spindle epithelial tumor with thymus-like differentiation of thyroid (SETTLE) is very rare neoplasm with 2 cellular forms, epithelial cell and spindle cell, and most reported cases have been in young people. An 11-year-old boy presented with painless swelling of the right neck lasting for more than 2 months. A tumor size measuring approximately 3 × 3 cm was resected, and intraoperative frozen pathology suggested a spindle cell tumor, which was confirmed as SETTLE by immunohistochemical staining and external hospital consultation. The immunohistochemical staining profile of the resected tumor tissue was as follows: cytokeratin (CK) (+), smooth muscle actin (weak+), vimentin (+), CK7 (focal+), B-cell lymphoma 2 (partial+), CD99 (-), calcitonin (+), galectin-3 (+), CK19 (+), and Ki-67 (10%+). Ultrasound at 1-year postoperative follow-up revealed no local recurrence of the lesion or lymph node metastasis in the thyroid gland. We summarized the disease characteristics of SETTLE among 6 cases reported to date and found that SETTLE is associated with a good prognosis and low postoperative recurrence rate. Thus, for this type of malignant thyroid tumor, diagnosis depends mainly on postoperative pathology and immunohistochemical staining and simple surgical resection is recommended.

Carcinoma showing thymus-like differentiation of the parotid gland: The brief report of cytomorphology and review of the literature

Here, we report an extremely rare case of carcinoma with thymus-like differentiation (CASTLE) of the parotid gland. CASTLE is a rare malignant epithelial tumor with thymic epithelial differentiation that arises in the thyroid gland or perithyroidal soft tissue. CASTLE of salivary gland origin is rare, with only nine published case reports to date (reported as "CASTLE" or "thymic carcinoma"). It is critical to diagnose salivary gland tumors using fine needle aspiration cytology. However, this tumor is rare, and there have been few studies on its cytomorphological features. Therefore, it is important to understand the cytological diagnostic characteristics of CASTLE. Herein, we review the cytological features and diagnostic characteristics of salivary gland CASTLE. We also report the genotype results obtained using targeted exome sequencing, which we analyzed with DNA extracted from formalin-fixed paraffin-embedded tissue.

Case report: Thymoid differentiated carcinoma of thyroid: Two cases

Objective

Thymoid carcinoma of the thyroid gland is a rare thyroid tumor, which is often presented in case reports.

Methods

The clinical data of two patients with thymic carcinoma of the thyroid gland were retrospectively reviewed.

Results

Case 1: a middle-aged woman who was admitted to the hospital because of "progressive enlargement of the anterior cervical mass for 8 months." Color Doppler ultrasound and CT showed malignant tumor with high possibility of bilateral cervical lymph node metastasis. Total thyroidectomy and bilateral central cervical lymph node dissection were performed. Lymph node biopsy showed the metastasis of small cell undifferentiated thyroid carcinoma. Because the biopsy pathological result was not consistent with the pathology of the primary lesion, immunohistochemistry was performed again, and the final diagnosis was thymic carcinoma in the thyroid gland. Case 2: the patient was an elderly man who was admitted to the hospital due to hoarseness for half a month. During the operation, the tumor invaded the trachea, esophagus, internal jugular vein, common carotid artery, and surrounding tissues. Palliative resection of the tumor was performed. The tumor postoperative pathology suggested thymoid carcinoma of the thyroid gland. It recurred and compressed the trachea 4 months after the operation, resulting in dyspnea of the patient, and finally tracheotomy was performed to alleviate the symptoms.

Conclusion

Case 1 showed multiple differences in pathological diagnosis, suggesting that the lack of specific imaging and clinical manifestations of thymoid-differentiated thyroid carcinoma made the diagnosis so difficult. Case 2 progressed rapidly, suggesting that thymoid-differentiated thyroid carcinoma was not always inert, and the treatment and follow-up should follow the principle of individualization.

Clinicopathological features and outcomes of intrathyroidal thymic carcinoma: a single institution study

Intrathyroidal thymic carcinoma (ITTC) is a rare malignancy of the thyroid. It is thought to originate from ectopic thymic tissue or embryonic thymic rest, in, or adjacent to, the thyroid. We analyzed the backgrounds, clinicopathological features, and prognosis of 20 patients with ITTC, treated at our hospital. Thirteen of the 15 patients (86%) who underwent ultrasonography were diagnosed as malignant, based on imaging findings. 16 of the 17 patients (93%) who underwent cytology, were diagnosed or suspected to be malignant. Locally curative surgery (thyroidectomy and lymph node dissection) was performed for 19 patients. Large tumor size (>4 cm) was positively related to pathological node metastasis (p = 0.0389). Fourteen patients, including nine Ex-positive patients, underwent adjuvant external beam radiotherapy (EBRT) of the neck after surgery. Two patients showed recurrence of thyroid bed after and neither of them underwent adjuvant EBRT after surgery. Two patients who underwent EBRT showed recurrences of the lateral nodes (level V and level II), but they were easily dissected by re-operation. Ten- and 20-year local recurrence-free survival rates were 84.9% and 60.6%, respectively. To date, four patients showed distant recurrence, and 10- and 20-year distant recurrence-free survival rates were 75.0% and 75.0%, respectively. Our findings indicate that 1) the prognosis of ITTC is generally favorable, and 2) large tumor size is significantly related to lymph node metastasis. Two patients showing recurrence of the central region did not undergo EBRT; thus, further comparative studies are desirable to elucidate whether EBRT can prevent significant local recurrence.

Primary Thyroid Neoplasm with Fetal Morphology Associated with DICER1 Mutations: Expanding the Diagnostic Profile of Thyroblastoma

Introduction: Thyroblastoma, a primary thyroid neoplasm with histological features of primitive thyroid tissue has recently been described and is included as a distinct entity in the most recent edition of the World Health Organization (WHO) Classification of Tumors (5th edition). In this study, we expand the clinical, morphological, and molecular profile of this aggressive neoplasm. Patient Findings: The patients are females, 19 and 45 years of age, referred for large thyroid nodules. Tumor morphology is biphasic, composed of nests and follicles of epithelial cells, some with colloid-like secretions reminiscent of fetal thyroid follicles intertwined with a primitive stromal spindle cell component. By immunohistochemistry, the epithelial component is diffusely positive for PAX8 and TTF1 markers. Molecular studies showed DICER1 aberrations. Conclusion: A primary primitive thyroid malignancy reminiscent of early fetal embryology with no teratoid element, recently reported as thyroblastoma represents a unique entity, novel in its description, and is likely underdiagnosed.

Thyroid Carcinoma Showing Thymus-like Differentiation (CASTLE): A Case Report

Background and Objectives: Carcinoma showing thymus-like differentiation (CASTLE) is a low-grade thyroid carcinoma, with an indolent clinical course and usually a favorable prognosis. The clinical and imagistic features are not specific for CASTLE but similar to other malignant lesions of the thyroid. Definite diagnosis is based on an immunohistochemical examination, as this carcinoma shows positive CD5 immunoreactivity when compared to other aggressive thyroid carcinomas. Case presentation: The main focus of this study is to outline a rare case of CASTLE compressing the trachea in a 50-year-old female patient who was initially diagnosed with undifferentiated thyroid carcinoma, for which she underwent unsuccessful surgery, as well as postoperative radiotherapy and chemotherapy. After receiving a second medical opinion, the patient underwent a challenging radical resection consisting in total thyroidectomy and central neck dissection, with no local recurrence after 6 months and 2 years of follow-up and negative metastatic follow-up. The correct diagnosis has been established based on pathological and immunohistochemical examinations. Conclusions: In summary, the diagnosis of CASTLE is difficult and requires an experienced histological analysis and CD5 immunoreactivity. Lack of metastasis, complete removal of the tumor, and a low degree of tumor infiltration into nearby structures are all associated with better long-term survival.

Case report and literature review: thyroid carcinoma showing intrathyroid thymic carcinoma

Background

Intrathyroid thymic carcinoma (ITTC) is a rare malignancy of the thyroid gland with histological and immunophenotypic resemblance to thymic carcinoma. Surgery combined with adjuvant radiotherapy improves the survival of patients with ITTC. However, for patients with extensive metastases, there is currently no effective treatment. Chemotherapy is an option but has not demonstrated improved patient survival.

Methods and results

A female patient presented with metastases to the pleura, lung, and bone 16 years after surgery for ITTC. As radiotherapy and chemotherapy failed to control the recurrent disease, lenvatinib treatment was initiated. After 3 months, positron emission tomography/computed tomography showed a substantial reduction of all metastatic lesions and decreased tumor metabolism. The patient continues to receive lenvatinib and remains well and symptom-free.

Conclusion

For patients with ITTC who have progressive, life-threatening metastases, lenvatinib represents a valuable salvage therapy that may offer a sustained reduction in tumor burden and maintenance of quality of life.

Genomic variation associated with carcinoma showing thymus-like elements (CASTLE) in thyroid gland

Background

Carcinoma showing thymus-like elements (CASTLE) is a rare kind of malignant tumor of thyroid gland. The genetic mutation characteristics of CASTLE are not clear.

Methods

We retrospectively analyzed seven patients diagnosed as CASTLE tumor in our hospital, and performed whole exome sequencing (WES) in five cases to analyze the genomic variation of CASTLE in thyroid gland.

Results

The diagnosis of CASTLE was confirmed by histopathological and immunohistochemical results. Immunohistochemical staining showed that cell membranes of tumor samples in all cases were moderately to strongly positive for CD5 and CD117. WES presented a large number of single nucleotide variants (SNVs), insertions and deletions (InDel), and copy number variations (CNVs). By comparing with the TCGA database, we found novel mutations in significantly mutated genes such as FBXL16, PAQR7, LEFTY1, UBA52, and FLNA, as well as in potential disease-related driver genes such as MLLT10, FLNA, CYLD, HLA-B, KMT2D, SFPQ, MUC16, EEF2, and KMT2C.

Conclusions

CASTLE tumors contain unique tumor driver gene mutations. The information about mutations in several novel genes obtained in this study may contribute to unraveling the molecular mechanisms responsible for the emergence of thyroid CASTLE tumors and help formulating possible in-roads for treatment.

Overview of the 2022 WHO Classification of Thyroid Neoplasms

This review summarizes the changes in the 5th edition of the WHO Classification of Endocrine and Neuroendocrine Tumors that relate to the thyroid gland. The new classification has divided thyroid tumors into several new categories that allow for a clearer understanding of the cell of origin, pathologic features (cytopathology and histopathology), molecular classification, and biological behavior. Follicular cell-derived tumors constitute the majority of thyroid neoplasms. In this new classification, they are divided into benign, low-risk, and malignant neoplasms. Benign tumors include not only follicular adenoma but also variants of adenoma that are of diagnostic and clinical significance, including the ones with papillary architecture, which are often hyperfunctional and oncocytic adenomas. For the first time, there is a detailed account of the multifocal hyperplastic/neoplastic lesions that commonly occur in the clinical setting of multinodular goiter; the term thyroid follicular nodular disease (FND) achieved consensus as the best to describe this enigmatic entity. Low-risk follicular cell-derived neoplasms include non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), thyroid tumors of uncertain malignant potential, and hyalinizing trabecular tumor. Malignant follicular cell-derived neoplasms are stratified based on molecular profiles and aggressiveness. Papillary thyroid carcinomas (PTCs), with many morphological subtypes, represent the BRAF-like malignancies, whereas invasive encapsulated follicular variant PTC and follicular thyroid carcinoma represent the RAS-like malignancies. This new classification requires detailed subtyping of papillary microcarcinomas similar to their counterparts that exceed 1.0 cm and recommends not designating them as a subtype of PTC. The criteria of the tall cell subtype of PTC have been revisited. Cribriform-morular thyroid carcinoma is no longer classified as a subtype of PTC. The term "Hürthle cell" is discouraged, since it is a misnomer. Oncocytic carcinoma is discussed as a distinct entity with the clear recognition that it refers to oncocytic follicular cell-derived neoplasms (composed of > 75% oncocytic cells) that lack characteristic nuclear features of PTC (those would be oncocytic PTCs) and high-grade features (necrosis and ≥ 5 mitoses per 2 mm²). High-grade follicular cell-derived malignancies now include both the traditional poorly differentiated carcinoma as well as high-grade differentiated thyroid carcinomas, since both are characterized by increased mitotic activity and tumor necrosis without anaplastic histology and clinically behave in a similar manner. Anaplastic thyroid carcinoma remains the most undifferentiated form; squamous cell carcinoma of the thyroid is now considered as a subtype of anaplastic carcinoma. Medullary thyroid carcinomas derived from thyroid C cells retain their distinct section, and there is a separate section for mixed tumors composed of both C cells and any follicular cell-derived malignancy. A grading system for medullary thyroid carcinomas is also introduced based on mitotic count, tumor necrosis, and Ki67 labeling index. A number of unusual neoplasms that occur in the thyroid have been placed into new sections based on their cytogenesis. Mucoepidermoid carcinoma and secretory carcinoma of the salivary gland type are now included in one section classified as "salivary gland-type carcinomas of the thyroid." Thymomas, thymic carcinomas and spindle epithelial tumor with thymus-like elements are classified as "thymic tumors within the thyroid." There remain several tumors whose cell lineage is unclear, and they are listed as such; these include sclerosing mucoepidermoid carcinoma with eosinophilia and cribriform-morular thyroid carcinoma. Another important addition is thyroblastoma, an unusual embryonal tumor associated with DICER1 mutations. As in all the WHO books in the 5th edition, mesenchymal and stromal tumors, hematolymphoid neoplasms, germ cell tumors, and metastatic malignancies are discussed separately. The current classification also emphasizes the value of biomarkers that may aid diagnosis and provide prognostic information.

A case of concurrent occurrence of carcinoma showing thymus-like differentiation and follicular variant of papillary thyroid cancer in the same thyroid

Carcinoma showing thymus-like differentiation (CASTLE) is a rare thyroid cancer. This is the first report of a case of concurrent occurrence of CASTLE with papillary thyroid carcinoma (PTC).

A 66-year-old male patient had hoarseness with right vocal cord paralysis. Ultrasonography revealed a hypoechoic nodule in the inferior pole of the right thyroid lobe. Ultrasound-guided fine-needle aspiration cytology suggested differentiated thyroid cancer. The patient underwent total thyroidectomy with neck dissection. Pathological examination revealed two different thyroid cancers: a CASTLE and a follicular variant of PTC. Postoperative radiation therapy was performed. The patient was still alive after 5 year following the initial treatment without evidence of recurrence. The oncological management of patients with concurrent occurrence of different thyroid cancers should consider the biological behavior of both tumors.

Intrasalivary Thymic Carcinoma: A Case Report and Literature Review

Ectopic thymic carcinomas are rarely diagnosed in the thyroid gland, let alone in extrathyroid tissues. In the currently available literature, only five cases of extrathyroidal malignancies with thymic differentiation have been reported as arising in the major salivary glands. A 69-year-old female presented with a slow-growing palpable mass in the left parotid gland. Fine needle aspiration biopsy suggested metastatic cancer, whereas core needle biopsy revealed high-grade squamous cell carcinoma. The patient underwent left radical parotidectomy with selective ipsilateral lymph node dissection and subsequent radiation therapy. The surgical specimen was taken for histopathological examination. Microscopically, the tumor resembled thymic carcinoma. It was composed of large nests of squamoid cells with smooth contours, focally with a syncytial growth pattern, and accompanied by abundant lymphocytes with reactive lymphoid follicles. This appearance resembled a micronodular thymic carcinoma with lymphoid hyperplasia. Moreover, the tumor displayed expression of squamous markers (p40 and p63) and markers of thymic carcinoma (CD5 and CD117). Therefore, the final diagnosis of intrasalivary thymic carcinoma was rendered. The molecular analysis including next-generation sequencing demonstrated no variants of the strong, potential, or unknown clinical significance. The patient remains disease-free at 1-year follow-up. In the current case, we comprehensively present a clinical, microscopic, molecular, and radiological picture of CD5-positive squamous cell carcinoma of the parotid. We postulate that similar cases should be designated as intrasalivary thymic carcinoma analogically to similar thyroid tumors. Our case and the limited literature data indicate they should be distinguished from conventional squamous cell carcinoma of major salivary glands due to their rather favorable prognosis.

Carcinoma showing thymus-like differentiation (CASTLE) of the salivary gland: Report of 2 cases of a hitherto under-recognized extrathyroid counterpart

Carcinoma showing thymus-like differentiation (CASTLE) outside the thyroid gland is extremely rare. Here we report two cases of CASTLE of the major salivary gland. The tumors occurred in the parotid gland of a 31-year-old female (Case 1) and in the submandibular gland of a 40-year-old female (Case 2). Both tumors showed a lobulated growth pattern, and were histologically composed of a nested or sheet-like proliferation of carcinoma cells with round- to oval-shaped nuclei, distinct nucleoli and pale eosinophilic cytoplasm, accompanied by various degrees of lymphocytic infiltration. Immunohistochemical staining revealed that the tumors were positive for pan-cytokeratin, p40, CD5, CD117 and bcl-2. In addition, PD-L1 expression was seen in 10-90% of tumor cells. After the initial surgery, Case 1 remained tumor-free for 20 months, while Case 2 suffered lymph node recurrence at 4 months, followed by lung metastasis, which was treated with chemoradiotherapy and anti-PD-1 immune checkpoint inhibitor, resulting in a partial response. The present findings indicate that an extrathyroid counterpart of CASTLE can occur as a primary salivary gland neoplasm. Salivary CASTLEs seem to show a wide range of biological behavior, and long-term follow-up may be needed. Immune checkpoint inhibitor targeting PD-1 might become a promising treatment option in patients with CASTLE; however, further study with a larger number of cases is necessary to establish the optimal therapeutic strategy and prognostic factors for this rare cancer.

Spindle epithelial tumor with thymus-like differentiation in fine needle aspiration of thyroid gland: Report of two cases

Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a rare, malignant tumor of the thyroid gland that typically affects young males and has a propensity for late metastasis. With fine needle aspiration (FNA) being a primary tool for diagnosis of thyroid lesions, there are rare reports of cytological features of SETTLE on FNA since its initial characterization 30 years ago . Here we report two cases of SETTLE, involving 9-year-old and 15-year-old male patients. Both patients underwent US-guided FNA with a subsequent resection confirming the diagnosis of SETTLE. In the first patient the thymic origin of the tumor was suspected on FNA, but the diagnosis of SETTLE was established only after resection. Five years later, this patient presented with an enlarged ipsilateral cervical lymph node. Needle biopsy confirmed it to be a metastatic tumor compatible with SETTLE. In the second patient the diagnosis of SETTLE was suggested on FNA. Cytology of the thyroid gland nodule on FNA from both patients showed loosely cohesive and single spindle-shaped epithelial cells associated with metachromatic stroma. The differential diagnosis of spindle cell lesions of the thyroid should include SETTLE based on characteristic morphological features, after more common entities of thyroid gland such as medullary carcinoma are excluded.

Recurrence of carcinoma showing thymus-like differentiation (CASTLE) involving the thyroid gland

BACKGROUND

Carcinoma showing thymus-like differentiation (CASTLE) in the thyroid gland is a rare disease with generally a favorable prognosis. Treatment with surgery and adjuvant radiotherapy has been shown to improve local control and long-term survival rates. In this report, we present a case of a recurrent thyroid gland CASTLE and review the literature on the diagnosis and treatment of this disease.

CASE PRESENTATION

A 60-year-old woman, who was diagnosed with a CASTLE thyroid tumor in 2015, had a total thyroidectomy and was maintained on thyroid hormone replacement (levothyroxine). After 5 years, the patient had a recurrence, in an advanced stage unsuitable for surgery. As the patient declined to undergo radiotherapy, she was followed up without intervention and is currently stable after 15 months.

CONCLUSIONS

CASTLE is a rare disease, diagnosed based on postoperative pathology and immunohistochemistry analysis, especially upon CD5 marker. In case of relapse, treatment options include surgery and radiotherapy; however conservative management without intervention is an acceptable alternative in some cases.

Inoperable CASTLE of the thyroid gland treated with radical radiotherapy with complete remission

Carcinoma showing thymus-like elements (CASTLE) is an extremely rare malignant tumor of the thyroid gland and soft tissues of the neck with favorable prognosis. Histological features of the CASTLE are similar to thymic carcinoma, and it is assumed that it arises from the ectopic thymic tissue or the remnants of branchial pouches. The optimal treatment strategy is still uncertain because of the rarity of the tumor. The mainstay of treatment is surgery. The role of other modalities is unclear. We present a case report of a patient with locally advanced CASTLE of the thyroid gland who was not suitable for surgery and underwent radical radiotherapy with subsequent achievement of complete remission. We also present a literature review.

A Rare Case of Thyroid Carcinoma Showing Thymus-Like Differentiation in a Young Adult

Thyroid carcinoma showing thymus-like differentiation (CASTLE) is thought to originate from ectopic thymic tissue or remnants of the developing thymus within or adjacent to the thyroid. This case report describes a mass located on the left thyroid of a 28-year-old man. Fine-needle aspiration cytology revealed a number of lymphoid cells without atypia that were similar to those seen in a malignant lymphoma of the thyroid, and surgery was performed. Based on additional histopathological findings, the tumor was finally diagnosed as a CASTLE. It is difficult to diagnose this neoplasm using fine-needle aspiration cytology. However, it is possible to differentially diagnose CASTLE based on its histological features. CD5 is useful for diagnosing CASTLE with immunohistochemical staining.

Spindle cell tumour with thymus-like differentiation (SETTLE) on fine needle aspiration cytology: A case report highlighting diagnostic pitfalls

A 7-year-old girl presented with a painless neck swelling localised near the left lobe of the thyroid gland, which was initially investigated by fine needle aspiration cytology. This raised a differential diagnosis of medullary thyroid carcinoma and small round blue cell tumour. Only after several additional clinical investigations and a total thyroidectomy was a definitive diagnosis of spindle cell tumour with thymus-like differentiation (SETTLE) reached. This case report highlights how contemporaneous clinical and investigation findings made arriving at a definitive diagnosis challenging, contributed to diagnostic delay, and ultimately influenced choice of treatment.

Role of immunoproteasomes and thymoproteasomes in health and disease

The proteasome is a multisubunit protease that degrades intracellular proteins into small peptides. Besides playing a pivotal role in many cellular processes indispensable for survival, it is involved in the production of peptides presented by major histocompatibility complex class I molecules. In addition to the standard proteasome shared in all eukaryotes, jawed vertebrates have two specialized forms of proteasome known as immunoproteasomes and thymoproteasomes. The immunoproteasome, which contains cytokine-inducible catalytic subunits with distinct cleavage specificities, produces peptides presented by class I molecules more efficiently than the standard proteasome. The thymoproteasome, which contains a unique catalytic subunit β5t, is a tissue-specific proteasome expressed exclusively in cortical thymic epithelial cells. It plays a critical role in CD8⁺ cytotoxic T cell development via positive selection. This review provides a brief overview on the structure and function of these specialized forms of proteasome and their involvement in human disease.

Resection of a Tumor With Thymic-like Differentiation and Reconstruction of the Innominate Artery

Carcinomas showing thymic-like differentiation (CASTLE tumors) are very rare entities requiring an individualized therapeutic plan. This report describes a case of reconstruction of the innominate artery after radical resection of the tumor in a patient in whom a custom-made cerebral shunt was used for continuous cerebral perfusion.

Whole exome sequencing and establishment of an organoid culture of the carcinoma showing thymus-like differentiation (CASTLE) of the parotid gland

Carcinoma showing thymus-like differentiation (CASTLE) is a rare tumor, especially in the parotid gland. We encountered a CASTLE of the parotid gland and analyzed its clinicopathological features, as well as the genotype using whole exome sequencing (WES). Moreover, we successfully established an organoid culture cell line from the primary tumor tissue. The patient was a 23-year-old woman who underwent superficial parotidectomy with peripheral neck dissection, followed by radiotherapy. Pathologically, the resected specimen showed atypical epithelioid nests and trabeculae with squamous differentiation, separated by thick fibrous septa, accompanied by dense lymphocytes and plasma cell infiltration. Immunohistochemistry revealed that the tumor cells were positive for AE1/AE3, p40, p63, p16, CK5/6, and CD5, and the background lymphocytes were positive for CD5 and CD99. Based on these findings, the tumor was diagnosed as CASTLE. WES uncovered five nonsynonymous and splicing somatic mutations, namely, FREM2 p.Val861Phe, CLK3 p.Phe376Leu, DLGAP1 p.Lys294Asn, NOX1 p.Val165Met, and PSG9 c.430 + 4A > T. Organoid culture cells preserved the histopathological characteristics of the epithelioid component of CASTLE and harbored all five somatic mutations detected in the primary tumor. In conclusion, for the first time to the best of our knowledge, we successfully analyzed a comprehensive genotype and established an organoid culture cell line of a parotid gland CASTLE, which should serve for analyzing the nature of this rare tumor.

Ectopic cervical thymoma with myasthenia gravis: a rare association

Thymic masses are one of the most common tumors in the anterior mediastinum. Nevertheless, because the thymus originates in the third and fourth pharyngeal pouches and descends into the anterior mediastinum, ectopic thymic tissue may be found anywhere from the angle of the mandible to the superior mediastinum. Ectopic cervical thymoma (ECT) is an extremely rare tumor that originates from ectopic thymic tissue trapped during the migration of the embryonic thymus and is often misdiagnosed as a thyroid tumor or other neck masses. Herein, we report an unusual case of ectopic cervical thymoma associated to myasthenia gravis (MG).

Pitfalls in Challenging Thyroid Tumors: Emphasis on Differential Diagnosis and Ancillary Biomarkers

Thyroid pathology encompasses a heterogenous group of clinicopathological entities including rare and diagnostically challenging neoplasms. The review is focused on morphological, immunohistochemical, and molecular features of rare thyroid neoplasms that can pose diagnostic problems. The tumors are organized based on growth patterns including thyroid neoplasms with predominantly papillary, follicular, solid, and spindle cell growth pattern, as well as neoplasms with distinct cytological characteristics. A special section is also dedicated to rare thyroid tumors with peculiar patterns including thyroid carcinoma with Ewing family tumor elements and intrathyroidal thymic-related neoplasms.

Carcinoma Showing Thymus-Like Differentiation (CASTLE) Arising in the Sublingual Gland

Carcinoma showing thymic-like differentiation (CASTLE) is a rare tumor most commonly occurring in the thyroid and soft tissues of the neck. We report the first case of CASTLE occurring in the sublingual gland. The patient, a 35-year-old healthy man, presented with a submucosal lesion located in the anterior right floor of the oral cavity and an ipsilateral neck mass. The lesion had been previously investigated by neck computed tomography and ultrasound-guided fine needle aspiration cytology and diagnosed as metastatic squamous cell carcinoma. After oral cavity magnetic resonance imaging, positron emission tomography, and a non-diriment, fine needle aspiration cytology of the sublingual mass, the patient was treated as affected by a sublingual gland malignancy with removal of primary tumor and neck dissection. Morphological and immunohistochemical findings were diagnostic for primary sublingual gland CASTLE. The patient received adjuvant radiotherapy and is free of disease 2 years after treatment. We describe the pathological features of the lesion and discuss the possible differential diagnoses.

Malignant teratoid tumor of the thyroid gland: an aggressive primitive multiphenotypic malignancy showing organotypical elements and frequent DICER1 alterations-is the term "thyroblastoma" more appropriate?

Primary thyroid teratomas are exceedingly rare. Mature and immature variants recapitulate their gonadal counterparts (predilection for infants/children, triphasic germ layer differentiation, and favorable outcome). On the other hand, the so-called malignant teratomas affect predominantly adults and elderly, are highly aggressive, and, according to a few published cases, harbor DICER1 mutations. We describe three highly aggressive sporadic malignant teratoid thyroid tumors in 2 females (17 and 45 years) and one male (17 years). Histology showed triphasic neoplasms composed of solid nests of small primitive monomorphic cells embedded in a cellular stroma with primitive immature rhabdomyosarcoma-like (2) or pleomorphic sarcoma-like (1) phenotype. The third component was represented by TTF1+/PAX8+ primitive teratoid epithelial tubules reminiscent of primitive thyroid follicles and/or Wilms tumor, admixed with scattered respiratory- or enteric-type tubules, neuroepithelial rosettes, and fetal-type squamoid nests. Foci of cartilage were seen in two cases, but none contained mature organoid adult-type tissue or skin adnexa. SALL4 was expressed in the small cell (2) and stromal (1) component. Other germ cell markers were negative. Molecular testing revealed a known “hotspot” pathogenic DICER1 mutation in two cases. In addition, case 1 had a missense TP53 variant. This type of thyroid malignancy is distinct from genuine teratomas. The immunoprofile suggests primitive thyroid- or branchial cleft-like differentiation. Given that “blastoma” is a well-accepted terminology in the spectrum of DICER1-associated malignancies, the term “thyroblastoma” might be more convenient for these malignant teratoid tumors of the thyroid gland. Relationship of thyroblastoma to the DICER1 syndrome remains to be addressed.

Biphenotypic Branchioma: A Better Name Than Ectopic Hamartomatous Thymoma for a Neoplasm with HRAS Mutation

Ectopic hamartomatous thymoma is a rare neck lesion originally thought to represent a non-neoplastic hamartoma, even though thymic origin has been questioned, and there is uncertainty about whether the lesion is a neoplasm. We investigated the genetics by performing targeted next generation sequencing (NGS). Three cases were identified from the authors' consultation files. A custom, targeted NGS panel including 1385 pan-cancer-related genes was performed on all cases. Three patients included 2 males and 1 female, aged 50, 58 and 70 years, respectively (mean 59.3 years), with tumors arising in the low anterior neck. All cases showed classical histologic features of EHT, with one case showing intraductal carcinoma in association with the EHT. By targeted NGS, one case harbored a hotspot HRAS mutation (p.Gln61Lys), while the other two cases only showed non oncogenic variants. Dual mesoderm and endoderm derivation/differentiation (biphenotypic) has been previously recognized, with epithelial and myoepithelial components, and arising from the apparatus contributing to neck development (branchial apparatus). Thus, EHT has been shown to have genetic alterations in HRAS. These findings, without evidence of thymic derivation or an ectopic tissue location, strongly support that EHT is a true neoplasm. The name biphenotyic branchioma more correctly reflects the true nature of this dual mesoderm and endoderm derived tumor occurring in the lower neck.

Thyroid Carcinoma Showing Thymus-Like Differentiation (CASTLE) with Tracheal Invasion: A Case Report

Patient: Male, 49-year-old

Final Diagnosis: Thyroid carcinoma showing thymus-like differentiation (CASTLE)

Symptoms: Hoarseness

Medication: —

Clinical Procedure: Thyroidectomy

Specialty: Surgery

Spindle Epithelial Tumor with Thymus-Like Differentiation (SETTLE): A Case Report

Background: Spindle epithelial tumor with thymus-like differentiation (SETTLE) is a tumor with an indolent disease course and late metastatic potential. It occurs primarily in children and adolescents, although it can present later in life. It was first described by Chan and Rosai [Tumors of the neck showing thymic or related branchial pouch differentiation: a unifying concept. Hum Pathol. 1991;22(4):349-67. doi:10.1016/0046-8177(91)90083-2], and there have been approximately 46 cases published in the English literature. Case report: We present an 8-year-old female with a SETTLE, undergoing an initial fine-needle aspiration and later a diagnostic biopsy. There is no evidence of disease recurrence at 3.5 years of follow-up. Conclusion: Though fine-needle aspirate biopsy is useful in directing the diagnostic workup of SETTLE by indicating concerning pathology, the broad differential diagnosis associated with it requires histology in conjunction with a limited immunohistochemical panel and unremarkable cytogenetics workup. Surgical resection is the main stay of treatment, and long-term follow-up is important in these patients.

[Ectopic thymic tissue and ectopic thymic tumors]

Ectopic thymic tissue outside its core position in the antero-superior mediastinum is quite common owing to the complexity of embryonal thymus development, whereby reported prevalence values (1 to 90%) are heavily dependent on the method of investigation and the intensity of the workup. The debated prevalence and relevance of ectopic thymic tissue and its accessibility underlie the ongoing discussion whether modern, minimally invasive thymectomy strategies can match the proven benefit of the radical transsternal thymectomy procedure for the treatment of Myasthenia gravis. In this context, the following article covers the etiology, prevalence, and location of normal-looking, reactive, and neoplastic ectopic thymic tissue. Furthermore, ectopic tissues and tumors inside or adjacent to the thymus are mentioned.

Pembrolizumab in a Patient With a Metastatic CASTLE Tumor of the Parotid

Carcinoma showing thymus-like elements (CASTLE) is a rare tumor, most commonly found in the thyroid gland. Here we report a case of CASTLE tumor localized to the parotid gland, recognized in retrospect after a late manifestation of symptomatic pleural carcinomatosis. The original tumor in the parotid gland was treated by surgery followed by radiotherapy. Ten years later, a metastatic disease with recurrent pleural effusions occurred. Pleural carcinomatosis was strongly positive for CD5, CD117, and p63 as was the original tumor of the parotid, which allowed the diagnosis of a CASTLE tumor. Additionally, the pleural tumor expressed high levels of programmed death ligand 1 (PD-L1), and the patient underwent treatment with the monoclonal PD-L1 inhibitor pembrolizumab achieving a partial remission. To the best of our knowledge, this is the first patient with a metastatic CASTLE tumor treated with a PD-L1 inhibitor.

The 'CASTLE' tumour: An extremely rare presentation of a thyroid malignancy. A case report

Thyroid carcinoma showing thymic-like differentiation (CASTLE) is a rare malignancy of the thyroid gland, and it accounts for 0.1–0.15% of all thyroid cancers. As the name suggests, it has a histological and immunophenotypic resemblance to thymic carcinoma. Preoperative diagnosis of CASTLE can be difficult as its clinical manifestations, and histological characteristic resembles other aggressive and advanced thyroid carcinomas. It is essential to distinguish CASTLE from other aggressive neoplasms as the former has a more favourable prognosis. Immunohistochemical staining with CD5 can help to differentiate thyroid CASTLE from other aggressive thyroid neoplasms.

Due to the rarity of this disease, there is no clear definitive treatment strategy. Surgical resection of CASTLE is usually attempted initially. Nodal involvement and extrathyroidal extension are shown to be the main prognostic factors that influenced the survival of patients. Therefore, complete resection of the tumour is vital to reduce local recurrence rates and to improve the chance of long-term survival. Radiotherapy (RT) for CASTLE is an effective treatment. Curative surgery followed by adjuvant RT should be considered in cases with extrathyroidal extension and nodal metastases. With RT, shrinkage of the tumour and reduction of local recurrence rate is possible.

With that in mind, we present a case of CASTLE who presented with airway compression symptoms three years after thyroid surgery. He subsequently underwent tumour debulking surgery and a tracheostomy. The patient refused adjuvant chemoradiotherapy, and during our serial follow-up, he is well and symptom-free.

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Thyroid carcinoma showing thymic-like differentiation (CASTLE) is a rare malignancy of the thyroid gland.

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Diagnosis of CASTLE can be difficult as it resembles other aggressive and advanced thyroid carcinomas.

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Immunohistochemical staining with CD5 can help to differentiate thyroid CASTLE from other aggressive thyroid neoplasms.

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Complete surgical resection is vital to reduce local recurrence rates and to improve the chance of long-term survival.

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Adjuvant radiotherapy should be considered in cases with extrathyroidal extension and nodal metastases.

A rare case of ectopic chest-wall thymoma: a case report

Ectopic extrathoracic thymoma is an uncommon clinical entity that has only been described sporadically, and most of them are ectopic hamartomatous thymomas or ectopic cervical thymomas. Here a case of 32-year-old woman with an ectopic thymoma was presented, which was found in right armpit and a postoperative diagnosis of 2018 World Health Organization (WHO) confirmed type B1, modified Masaoka stage I tumor was obtained. The patient had no symptoms of myasthenia or other immune disorders but once misdiagnosed as supernumerary breast. Tumor resection was performed and the tumor was completely removed. To our knowledge, this is a novel report that ectopic thymoma exists on chest wall and type B1 was confirmed according to 2018 WHO histological classification.