Carcinoma showing thymus-like elements (CASTLE) with amyloid deposition in the parotid gland

Carcinoma showing thymus-like elements (CASTLE) is a rare tumor that commonly occurs in the thyroid gland. Extrathyroidal CASTLE is rarer, and only 11 cases of CASTLE of major salivary glands have been reported to date. We report the first case of amyloid deposition in parotid CASTLE. A 63-year-old man presented with a slowly growing mass in the left parotid region. Computed tomography revealed an approximately 28 × 23 mm mass lesion in the left parotid gland, and squamous cell carcinoma was suspected on biopsy. The patient underwent a parotidectomy with neck dissection. Morphologically, the tumor cells were squamoid and formed nests with lymphoid infiltration. Immunohistochemically, the tumor cells exhibited immunoreactivity for CD5, CD117/c-kit and Bcl-2, p40, and CK5 but not for p16. We diagnosed the tumor as parotid CASTLE. Amyloid deposition was also observed in the primary tumor and metastatic lymph node lesions, which were immunoreactive for cytokeratin 5. Tumor cytokeratin-derived amyloid deposition may be one of characteristics of parotid CASTLE.

Expression of CD5 in salivary gland tumors: an ancillary marker for carcinoma showing thymus-like differentiation (CASTLE) of the major salivary gland

Recently, cases of carcinoma showing thymus-like differentiation (CASTLE) occurring in major salivary glands have been identified. To assess the diagnostic value of CD5 immunohistochemistry in distinguishing salivary CASTLE from other types of salivary gland tumors, we evaluated CD5 expression in 109 salivary gland tumors, encompassing 23 different histological types, including salivary CASTLE. In addition, we reviewed 10 previously reported cases of salivary CASTLE. Most salivary CASTLE cases (10/11, 91%) showed strong CD5 expression. In contrast, 104 of 108 (96%) non-salivary CASTLE tumors were negative for CD5, while the remaining four tumors (3.7%), all of which were histologically Warthin tumors, showed focal positivity for CD5 with weak to moderate intensity. In conclusion, the findings in this study support the potential use of CD5 immunohistochemistry for distinguishing salivary CASTLE from other histological types of salivary gland tumors. Aberrant CD5 expression in this tumor may be linked to the tumor microenvironment.

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.

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.

Ectopic Cervical Thymoma: An Uncommon Entity

Thymomas originates from the epithelial cells of thymic tissue. These tumors commonly occur in the anterior mediastinum. However, thymomas can arise anywhere from the aberrant or remnant thymus in the neck or mediastinum. Ectopic cervical thymoma is a rare disease. It is important to be aware that cervical masses can also be thymomas rather than thyroid or parathyroid masses. Here, we present a case of a 62-year-old female who presented with swelling in the neck and was diagnosed with cervical thymoma type AB.

Failure pattern and suggestions for target volume delineation of carcinoma showing thymus-like differentiation treated with intensity-modulated radiotherapy

BACKGROUND

To review our long-term clinical experience, analyze the failure patterns, and give suggestions for target volume delineation of carcinoma showing thymus-like differentiation (CASTLE) treated with intensity-modulated radiotherapy (IMRT).

METHODS

From April 2008 to May 2019, 30 patients with CASTLE treated by postoperative or radical IMRT in our center were retrospectively reviewed. A total dose of 56-60 Gy in 28-30 fractions was prescribed to patients without residual disease and 66 Gy in 33 fractions for patients with residual or unresectable disease. Survival rates were calculated using the Kaplan-Meier method. Treatment-related toxicities were graded by National Cancer Institute Common Toxicity Criteria (NCI-CTC) version 4.0.

RESULTS

Among the 30 patients, 12 (40%) received partial resection or biopsy. Lateral lymph node metastasis was observed in 7 (23.3%) patients. During follow-up, regional lymph node recurrence occurred in 2 patients and distant metastasis in 5 patients. With a median follow-up time of 63.5 months, the 5-year local recurrence-free survival (LRFS), regional recurrence-free survival (RRFS), distant metastasis-free survival (DMFS), overall survival (OS) and progression-free survival (PFS) rates were 100, 88.9, 78.9, 93.1 and 78.9%, respectively. For patients with no lateral neck node metastasis, prophylactic radiotherapy for lateral neck nodal regions failed to improve RRFS (p = 0.381) and OS (p = 0.153).

CONCLUSION

Distant metastasis was the major failure pattern for CASTLE after surgery and IMRT. For patients with no lateral neck node metastasis, the omission of irradiation for lateral neck nodal regions seems to be safe and feasible.

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.

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.

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.

Intrathyroidal thymic carcinoma misdiagnosed as a medullary thyroid carcinoma

The intrathyroidal thymic carcinoma is a rare neoplasm. The probable origin of this neoplasm is the presence of ectopic thymic tissue or remnants of the third and fourth branchial arch. The case of a 49-year-old female with an initial diagnosis of medullary thyroid cancer is presented. When she was operated for regional recurrence, 16 years later, the pathology report demonstrates the presence of a intrathyroidal thymic carcinoma. Intrathyroidal thymic carcinoma is considered an independent type of thyroid carcinoma because this entity has specific clinical-pathological characteristics similar to thymic carcinomas and different prognosis than known thyroid carcinomas. We present the case of a patient initially treated as having a medullary thyroid carcinoma who, upon presenting recurrence, the presence of intrathyroidal thymic carcinoma was demonstrated.

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.

Spindle epithelial tumour with thymus-like differentiation: report of two cases

Spindle epithelial tumour with thymus-like differentiation (SETTLE) is a very rare neck malignancy arising from thymic tissue or branchial pouch, mostly seen in the early decades of life. SETTLE is thought to be a low-grade neoplasm but distant metastases have been reported. Fewer than 50 cases have been reported in the PubMed database. We report on the four-year follow-up for a 13-year-old boy, with no signs of recurrence or distant metastasis. In addition, a 45-year-old woman was admitted to hospital with neck mass. Fine-needle aspiration biopsy was compatible with medullary thyroid carcinoma but serum levels of calcitonin were normal. Total thyroidectomy and central compartment lymph node dissection was planned with an initial diagnosis of medullary thyroid carcinoma. At surgery, frozen section analysis converted our diagnosis to SETTLE and the intraoperative strategy was changed. SETTLE should be considered in a patient with normal serum calcitonin levels in the presence of suspicious medullary thyroid carcinoma at fine-needle aspiration biopsy. Frozen section analysis may help to manage the intraoperative strategy. This report describes the first case of SETTLE successfully diagnosed by frozen section analysis.

Carcinoma Showing Thymus-Like Elements: A Rare Malignant Tumor of the Thyroid Gland

Carcinoma showing thymus-like elements (CASTLE) is a rare tumor arising in the thyroid gland. Fewer than 100 patients with this tumor, those predominantly from Eastern Asia, have been reported before. We present the first CASTLE case from Turkey. A 51-year-old male was admitted with a complaint of a neck mass and hoarseness. A laryngoscopic examination revealed left vocal cord paralysis. Neck ultrasonography showed a tumor which was compressing the esophagus and had invaded the left recurrent laryngeal nerve (RLN). The patient underwent a total thyroidectomy, a unilateral central-compartment neck dissection, and following adjuvant radiotherapy. Intraoperative nerve monitoring was performed during the operation to preserve the contralateral nerve. He completed a 3-year follow-up period after the completion radiotherapy, and no recurrence was observed. The treatment is controversial, although surgery with or without adjuvant radiotherapy appears to be the best choice. In cases of RLN destruction due to tumor invasion, we recommend using intraoperative nerve monitoring to preserve the contralateral RLN to avoid devastating complications, such as a tracheostomy.

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.

•

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

•

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

•

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

•

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

•

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

Management and Prognostic Factors for Thyroid Carcinoma Showing Thymus-Like Elements (CASTLE): A Case Series Study

Introduction: This study aims to identify the prognostic factors that influence therapeutic modalities for thyroid carcinoma showing thymus-like elements (CASTLE).

Materials and Methods: Reported studies with CASTLE patients published between 2004 and 2018 were retrieved from a cross-database literature search. Three patients treated in our institute were also included as one case series. Standardized data collection was performed; data pertaining to clinical stages, treatment regimens, and survival time were collected and statistically analyzed.

Results: Up to 26 case series of CASTLE were selected, including 51 males and 38 females with a median age of 48 years. Follow-up time ranged from 2 to 362 months and the median survival time was 158.03 months. Lymph node metastasis and tumor invasion of adjacent tissue both showed a significant negative effect on survival (p = 0.001 and 0.013, respectively). Radiotherapy significantly improved survival (p = 0.034), while neck dissection significantly prolonged survival only in patients with extrathyroidal extension (p = 0.043).

Conclusions: Extrathyroidal infiltration and nodal metastasis are important factors in cancer outcomes. Radiation therapy appears to be important for better outcomes in CASTLE patients, and neck dissection is recommended for patients with extrathyroidal extension.

Clinical outcome of intensity modulated radiotherapy for carcinoma showing thymus-like differentiation

PURPOSE

To evaluate the efficacy and toxicity of adjuvant intensity-modulated radiotherapy (IMRT) after surgery for carcinoma showing thymus-like differentiation (CASTLE).

METHODS

Between September 2008 and June 2015, 14 CASTLE patients were retrospectively enrolled. The clinical features, treatment procedure and clinical outcomes were reviewed. All patients received postoperative IMRT. The radiation doses ranged from 56Gy/28 fractions to 66Gy/33 fractions. Treatment-related toxicities were graded by National Cancer Institute Common Toxicity Criteria (NCI-CTC) version 3.0.

RESULTS

After a median follow-up period of 42 months, only one patient suffered local recurrence and distant metastasis. The most frequently seen acute toxicities were mucositis and dermatitis (grade 1-2). No grade 3-4 toxicities were observed.

CONCLUSIONS

Although based upon a small series of consecutively treated patients, our study showed that adjuvant IMRT provides satisfactory local-regional control for CASTLE, with acceptable toxicities. Further studies are still warranted to clarify our findings.

Carcinoma showing thymus like elements: Report of a case with EGFR T790M mutation

Carcinoma showing thymus-like differentiation of the thyroid (CASTLE) is a rare tumor involving the thyroid and perithyroidal soft tissues. It shares morphological, immunohistochemical and molecular similarities with thymic carcinomas. Due to its relatively better prognosis, it needs differentiation from other primary and metastatic tumors of this region. A 40-year-old lady presented with a gradually progressive anterior neck swelling for one year. Imaging showed bulky right and left lobes of thyroid along with a solid soft tissue mass in the pretracheal region. Fine needle aspiration smears showed features of poorly differentiated carcinoma. Total thyroidectomy with excision of the mass revealed histopathological features characteristic of CASTLE, with evidence of thyroiditis in adjoining thyroid. Epidermal growth factor receptor (EGFR) assay revealed presence of EGFR T790M somatic mutation in exon 20. The same was not detectable on direct sequencing. We present a rare case of CASTLE, occurring in association with Hashimoto thyroiditis, with emphasis on cytological features and report for the first time the presence of a low level somatic mutation in EGFR (EGFR T790M mutation).

CASTLE Thyroid Tumor: A Case Report and Literature Review

Carcinoma showing thymus-like differentiation is a rare tumor of the thyroid gland, which is structurally similar to thymic tissue. Overall, it has a favorable prognosis. Radiotherapy has been shown to be an effective local treatment, but there have been reports of distant recurrence. It has been suggested that adding chemotherapy may decrease the risk of recurrence. Here, we present a case report of a patient with a large tumor and extrathyroidal extension. The patient was treated with surgery, radiotherapy, and cisplatin with acceptable toxicity. The patient is free of locally recurrent or distant disease at 3 years.

Sonographic findings in three cases of carcinoma showing thymus-like differentiation

Carcinoma showing thymus-like differentiation (CASTLE) is a rare tumor of the thyroid gland or soft tissues of the head and neck. To our knowledge, there have been only a few reports concerning imaging findings of CASTLE. We report herein the sonographic appearances of three cases of CASTLE. Two tumors were located at the lower part of the thyroid and one had spread throughout the thyroid. Sonograms showed heterogeneously solid tumors without cystic components or calcification. The central part of the tumor was slightly hyperechoic compared with the peripheral part of the tumor. Histologically, the tumors were composed of a mixture of fibrous stroma and epithelial nests.