Review of clinical and diagnostic imaging of the thymus: from age-related changes to thymic tumors and everything in between

The thymus, a primary lymphoid organ of the immune system, undergoes several changes due to a variety of reasons, ranging from aging to pathological conditions. These changes can make distinguishing between benign and neoplastic changes in the thymus challenging, thereby complicating the histopathological diagnoses of thymic tumors. Moreover, most patients with thymic tumors are asymptomatic at the time of diagnosis. Therefore, imaging plays an extremely important role in the evaluation of thymic lesions. In this review, we introduced the imaging characteristics of the thymus, ranging from benign findings, such as normal maturation and benign lesions, to neoplasms.

Unraveling the Natural History of Good's Syndrome: A Progressive Adult Combined Immunodeficiency

BACKGROUND

Good's syndrome (GS) is a rare immune deficiency described almost 6 decades ago. Despite numerous published individual case reports and data collected in cross-sectional studies of small cohorts, the natural history and long-term outcomes of this disease remain unknown.

OBJECTIVE

We aimed to determine the clinical and laboratory evolution of 8 adults diagnosed with GS and consecutively evaluated between 1983 and 2023.

METHODS

In this prospective, longitudinal cohort study, newly diagnosed patients with GS were followed through repeated measures of clinical, immune, and hematologic changes, as well as targeted genetic screening.

RESULTS

All patients reported a healthy childhood and adolescence with symptom onset during the third or fourth decade of life. All presented to our center with recurrent bacterial sinopulmonary infections, thymoma, hypogammaglobulinemia, and absence of B cells. The median age of GS diagnosis was 57 years. During follow-up, immunoglobin replacement therapy effectively minimized sinopulmonary infections. However, the majority experienced severe and systemic viral or fungal infections, 3 developed basal cell carcinomas, and 5 had progressive bronchiectasis and persistent splenomegaly. The most notable clinical feature was opportunistic infections and in vitro evidence of cellular immune deficiency, which resulted in the death of 2 individuals. We also report a statistically significant, multidecade progressive decline in lymphocytes, platelets, hemoglobin, and red blood cells in our cohort, suggesting gradual bone marrow failure.

CONCLUSIONS

Knowledge of the unique phenotype and temporal evolution of GS has allowed us to develop a more comprehensive diagnostic framework. It can be investigated as part of broader research into disease pathophysiology.

Resection and a rare type of reconstruction of the superior vena cava with the left brachiocephalic vein

Resection and reconstruction of the superior vena cava (SVC) are required in a selected group of patients with anterior mediastinal tumors and lung neoplasms. We present the case of a 63-year-old woman who underwent invasive type B2 thymoma resection and a rare type of reconstruction of the superior vena cava using a patch of the left brachiocephalic vein (LBV). The various types of reconstruction of the superior vena cava are discussed.

Distribution of multi-level B cell subsets in thymoma and thymoma-associated myasthenia gravis

B-cell subsets in peripheral blood (PB) and tumor microenvironment (TME) were evaluated to determine myasthenia gravis (MG) severity in patients with thymoma-associated MG (TMG) and the distribution of B cells in type B TMG. The distribution of mature B cells, including Bm1-Bm5, CD19+ and CD20+ B cells and non-switched (NSMBCs) and switched (SMBCs) memory B cells, were determined in 79 patients with thymoma or TMG. Quantitative relationships between the T and TMG groups and the TMG-low and TMG-high subgroups were determined. NSMBCs and SMBCs were compared in TME and PB. Type B thymoma was more likely to develop into MG, with types B2 and B3 being especially associated with MG worsening. The percentage of CD19+ B cells in PB gradually increased, whereas the percentage of CD20+ B cells and the CD19/CD20 ratio were not altered. The (Bm2 + Bm2')/(eBm5 + Bm5) index was significantly higher in the TMG-high than in thymoma group. The difference between SMBC/CD19+ and NSMBC/CD19+ B cell ratios was significantly lower in the thymoma than TMG group. NSMBCs assembled around tertiary lymphoid tissue in thymomas of patients with TMG. Few NSMBCs were observed in patients with thymoma alone, with these cells being diffusely distributed. MG severity in patients with TMG can be determined by measuring CD19+ B cells and Bm1-Bm5 in PB. The CD19/CD20 ratio is a marker of disease severity in TMG patients. Differences between NSMBCs and SMBCs in PB and TME of thymomas can synergistically determine MG severity in patients with TMG.

Metabolic signatures of thymomas: potential biomarkers and treatment targets

OBJECTIVES

A study of tumour metabolic reprogramming has revealed disease biomarkers and avenues for therapeutic intervention. Metabolic reprogramming in thymoma is currently understudied and largely unknown. This study utilized metabolomics and isotope tracing with 13C-glucose to metabolically investigate thymomas, adjacent thymic tissue and benign thymic lesions.

METHODS

From 2017 to 2021, 20 patients with a suspected thymoma were recruited to this prospective Institutional Review Board approved clinical trial. At the time of surgery, 11 patients were infused with 13C-glucose, a stable, non-radioactive tracer which reports the flow of carbon through metabolic pathways. Samples were analysed by mass spectrometry to measure the abundance of >200 metabolites.13C enrichment was measured in patients who received 13C-glucose infusions.

RESULTS

Histological analysis showed that 9 patients had thymomas of diverse subtypes and 11 patients had benign cysts. In our metabolomic analysis, thymomas could be distinguished from both adjacent thymus tissue and benign lesions by metabolite abundances. Metabolites in pyrimidine biosynthesis and glycerophospholipid metabolism were differentially expressed across these tissues.13C-glucose infusions revealed differential labelling patterns in thymoma compared to benign cysts and normal thymus tissue. The lactate/3PG labelling ratio, a metabolic marker in aggressive lung tumours correlated with lactate uptake, was increased in thymomas (1.579) compared to normal thymus (0.945) and benign masses (0.807) (thymic tissue versus tumour P = 0.021, tumour versus benign P = 0.013).

CONCLUSIONS

We report metabolic biomarkers, including differential 13C labelling of metabolites from central metabolism, that distinguish thymomas from benign tissues. Altered glucose and lactate metabolism warrant further investigation and may provide novel therapeutic targets for thymoma.

Characteristics and outcome of systemic treatment for metastatic or unresectable thymic carcinoma: A single institution experience

BACKGROUND

Thymic carcinoma is a rare disease with an incidence of around 0.5 cases per million with a poor prognosis. The aim of this study was to assess patient outcomes with advanced thymic carcinoma receiving first-line chemotherapy.

METHODS

In our retrospective cohort study, we included patients who underwent treatment for metastatic thymic carcinoma between January 2013 to December 2019 in our hospital. Overall survival, progression-free survival (PFS), objective response rates (ORR) and chemotherapy regimens were assessed and analyzed.

RESULTS

A total of 27 patients were retrospectively analyzed. All patients received a platinum (cisplatin or carboplatin) based regimen as first-line chemotherapy (29.6% received ADOC, 11.1% received PE, 40.7% received CP, 14.8% received CAP). The median PFS on first-line chemotherapy was 199 days. The response rate was 40.7%. Median overall survival (OS) was 585 days. Positive CD5 staining was associated with better PFS.

CONCLUSION

We highlight the critical role of platinum-based chemotherapy agents as a primary treatment modality in advanced thymic carcinoma, underscoring the efficacy of platinum as a first-line option for recurrent disease, even in cases previously treated with platinum. Additionally, our findings indicate that CD5 positivity could be associated with improved PFS, suggesting its potential as a prognostic marker.

Disseminated thymoma in pleural fluid: An unusual case

Thymic epithelial tumours show characteristic cytological features on fine-needle aspiration cytology, however the cytological features of thymoma in fluid cytology are not well described. We present the case of a 77 year-old-woman with known pleural dissemination of type B2/B3 thymoma presenting with shortness of breath and orthopnoea due to a pleural effusion. Cytological evaluation of the pleural fluid showed cellular smears composed of numerous small lymphocytes with small numbers of admixed mesothelial cells. There was no epithelial component. On immunohistochemical (IHC) staining the lymphocytes were T cells which were positive for CD3. CD1a and terminal deoxynucleotide transferase (TdT) were also positive, consistent with immature lymphocytes of thymic origin. Despite the lack of an epithelial component, this case was diagnosed as suspicious for recurrent/ metastatic thymoma. This is only the second published case of thymoma identified on pleural fluid cytology, and to our knowledge the first case describing thymoma in pleural fluid with no epithelial component, a potential pitfall with the more common differential diagnosis of a reactive lymphocytic effusion.

The Molecular Landscape of Thymic Epithelial Tumors: A Comprehensive Review

Thymic epithelial tumors (TETs) are characterized by their extreme rarity and variable clinical presentation, with the inadequacy of the use of histological classification alone to distinguish biologically indolent from aggressive cases. The utilization of Next Generation Sequencing (NGS) to unravel the intricate genetic landscape of TETs could offer us a comprehensive understanding that is crucial for precise diagnoses, prognoses, and potential therapeutic strategies. Despite the low tumor mutational burden of TETS, NGS allows for exploration of specific genetic signatures contributing to TET onset and progression. Thymomas exhibit a limited mutational load, with prevalent GTF2I and HRAS mutations. On the other hand, thymic carcinomas (TCs) exhibit an elevated mutational burden, marked by frequent mutations in TP53 and genes associated with epigenetic regulation. Moreover, signaling pathway analyses highlight dysregulation in crucial cellular functions and pathways. Targeted therapies, and ongoing clinical trials show promising results, addressing challenges rooted in the scarcity of actionable mutations and limited genomic understanding. International collaborations and data-sharing initiatives are crucial for breakthroughs in TETs research.

GTF2I mutation in micronodular thymoma with lymphoid stroma

AIMS

Micronodular thymoma with lymphoid stroma is a rare subtype of thymoma with characteristic clinical and pathological features. Some of the features, such as indolent nature, principally spindle morphology and no significant association to myasthenia gravis, are shared with type A and AB thymoma, which is closely linked to GTF2I mutation. However, not much is known regarding the molecular genetics of this thymoma subtype. In this study, the GTF2I mutation status was investigated in 16 cases of micronodular thymoma.

METHODS

16 micronodular thymomas were retrieved and the GTF2I mutation was tested by Sanger sequencing. The clinicopathological findings were documented.

RESULTS

GTF2I c.1271T>A p.(Leu424His) mutation within exon 15 was detected in 14 out of 16 tumours (87.5%). Two patients died of other causes while all others remained alive with no evidence of recurrence during the follow-up period ranging from 19 to 188 months (median: 100 months).

CONCLUSIONS

GTF2I mutation status and presence of spindle cell morphology may indicate that type A and AB thymoma, and micronodular thymoma represent a group biologically distinct from type B thymomas, which generally lack this mutation.

Clinical study of thoracoscopic assisted different surgical approaches for early thymoma: a meta-analysis

OBJECTIVE

The efficacy and safety of subxiphoid thoracoscopic thymectomy (SVATS) for early thymoma are unknown. The purposes of this meta-analysis were to evaluate the effectiveness and safety of SVATS for early thymoma, to compare it with unilateral intercostal approach video thoracoscopic surgery (IVATS) thymectomy, and to investigate the clinical efficacy of modified subxiphoid thoracoscopic thymectomy (MSVATS) for early anterior mediastinal thymoma.

METHODS

Original articles describing subxiphoid and unilateral intercostal approaches for thoracoscopic thymectomy to treat early thymoma published up to March 2023 were searched from PubMed, Embase, and the Cochrane Library. Standardized mean differences (SMDs) and 95% confidence intervals (CIs) were calculated and analyzed for heterogeneity. Clinical data were retrospectively collected from all Masaoka stage I and II thymoma patients who underwent modified subxiphoid and unilateral intercostal approach thoracoscopic thymectomies between September 2020 and March 2023. The operative time, intraoperative bleeding, postoperative drainage, extubation time, postoperative hospital stay, postoperative visual analog pain score (VAS), and postoperative complications were compared, and the clinical advantages of the modified subxiphoid approach for early-stage anterior mediastinal thymoma were analyzed.

RESULTS

A total of 1607 cases were included in the seven studies in this paper. Of these, 591 cases underwent SVATS thymectomies, and 1016 cases underwent IVATS thymectomies. SVATS thymectomy was compared with IVATS thymectomy in terms of age (SMD = - 0.09, 95% CI: -0.20 to - 0.03, I2 = 20%, p = 0.13), body mass index (BMI; SMD = - 0.10, 95% CI: -0.21 to - 0.01, I2 = 0%, p = 0.08), thymoma size (SMD = - 0.01, 95% CI: -0.01, I2 = 0%, p = 0.08), operative time (SMD = - 0.70, 95% CI: -1.43-0.03, I2 = 97%, p = 0.06), intraoperative bleeding (SMD = - 0.30. 95% CI: -0.66-0.06, I2 = 89%, p = 0.10), time to extubation (SMD = - 0.34, 95%CI: -0.73-0.05, I2 = 91%, p = 0.09), postoperative hospital stay (SMD = - 0.40, 95% CI: -0.93-0.12, I2 = 93%, p = 0.13), and postoperative complications (odds ratio [OR] = 0.94, 95% CI: 0.42-2.12, I2 = 57%, p = 0.88), which were not statistically significantly different between the SVATS and IVATS groups. However, the postoperative drainage in the SVATS group was less than that in the IVATS group (SMD = - 0.43, 95%CI: -0.84 to - 0.02, I2 = 88%, p = 0.04), and the difference was statistically significant. More importantly, the postoperative VAS was lower in the SVATS group on days 1 (SMD = - 1.73, 95%CI: -2.27 to - 1.19, I2 = 93%, p < 0.00001), 3 (SMD = - 1.88, 95%CI: -2.84 to - 0.81, I2 = 97%, p = 0.0005), and 7 (SMD = - 1.18, 95%CI: -2.28 to - 0.08, I2 = 97%, p = 0.04) than in the IVATS group, and these differences were statistically significant. A total of 117 patients undergoing thoracoscopic thymectomy for early thymoma in the Department of Thoracic Surgery of the Second Hospital of Jilin University were retrospectively collected and included in the analysis, for which a modified subxiphoid approach was used in 42 cases and a unilateral intercostal approach was used in 75 cases. The differences between the two groups (MSVATS vs. IVATS) in general clinical characteristics such as age, sex, tumor diameter, Masaoka stage, Word Health Organization (WHO) stage, and intraoperative and postoperative conditions, including operative time, postoperative drainage, extubation time, postoperative hospital stay, and postoperative complication rates, were not statistically significant (p > 0.05), while BMI, intraoperative bleeding, and VAS on postoperative days 1, 3, and 7 were all statistically significant (p < 0.05) in the MSVATS group compared with the IVATS group.

CONCLUSION

The meta-analysis showed that the conventional subxiphoid approach was superior in terms of postoperative drainage and postoperative VAS pain scores compared with the unilateral intercostal approach. Moreover, the modified subxiphoid approach had significant advantages in intraoperative bleeding and postoperative VAS pain scores compared with the unilateral intercostal approach. These results indicate that MSVATS can provide more convenient operation conditions, a better pleural cavity view, and a more complete thymectomy in the treatment of early thymoma, indicating that is a safe and feasible minimally invasive surgical method.

Histogram analysis based on unenhanced CT for identifying thymoma and lymphoma among prevascular mediastinal incidentalomas

OBJECTIVE

To determine whether histogram analysis based on unenhanced CT can play a role in the differential diagnosis of thymoma and lymphoma from thymic hyperplasia and cyst (mean CT attenuation > 10 HU).

MATERIALS AND METHODS

This retrospective study included consecutive asymptomatic participants who have prevascular mediastinal lesions incidentally detected by unenhanced CT between December 2013 and August 2020, and with definitive diagnosis by pathology or additional radiologic work-ups. A total of thirteen histogram parameters on enhanced CT were calculated for each lesion, then were compared between tumor (thymoma + lymphoma) and non-tumor (hyperplasia + cyst). Receiver operating characteristic analysis was conducted to investigate the performance of histogram parameter for identifying tumor.

RESULTS

The study population included 192 patients (106 men and 86 women) with a mean age of 50.5 years at the time of CT examination. Of them, 94 patients have tumor (87 thymomas and 7 lymphoma) and 98 have non-tumor (48 thymic hyperplasia and 50 cysts). Nine of the thirteen histogram parameters revealed significant difference between the two groups, including median, minimum, range, 10th percentile, 90th percentile, kurtosis, skewness, uniformity and entropy. No significant difference was observed in the mean CT attenuation between groups. Higher median was found to be independent predictors for distinguishing tumor from non-tumor, and can achieve an area under the curve (AUC) of 0.785 (95% confidence interval [95% IC], 0.720-0.841).

CONCLUSIONS

Histogram analysis based on unenhanced CT may be able to provide some help in the differential diagnosis of incidental lesions in prevascular mediastinal.

GRAND SUPPORT

This study was sponsored by Natural Science Foundation of Shanghai (No. 21ZR1459700).

Thymic epithelial tumours: histopathological classification and differential diagnosis

The epithelial and lymphoid compartments of the thymus can give rise to a wide variety of tumours, including thymomas, thymic carcinomas, lymphoreticular proliferations, germ cell tumours, and sarcomas. While some of these have close similarity to their counterparts in other organs, both in terms of histology and immunohistochemistry, as well as molecular features, others are unique to the thymus. The epithelial tumours, which can develop in the thymus, will be discussed in this review, with a particular emphasis on resolving differential diagnosis by means of morphology, immunohistochemical profiles, and molecular diagnostics.

Benign lesions of the mediastinum

Mediastinal tumours represent a heterogeneous group of entities derived from the manifold structures located in or adjacent to the mediastinum. Due to the occurrence of some of these tumours in characteristic mediastinal compartments, an anatomical subdivision of the mediastinum in the prevascular (anterior), visceral (middle), and paravertebral (posterior) is helpful for the differential diagnosis. Benign anterior mediastinal tumours linked to an enlargement of the thymic gland mainly consist of thymic cysts and several types of thymic hyperplasia: true thymic hyperplasia, rebound hyperplasia, lymphofollicular hyperplasia, and so-called thymic hyperplasia with lymphoepithelial sialadenitis (LESA)-like features. Mature teratomas, ectopic (para)thyroid tissue, and benign thymic tumours such as thymolipoma or thymofibrolipoma represent further typical tumours of the anterior mediastinum. Pericardial, bronchogenic, or oesophageal duplication cysts predominate in the middle mediastinum, whereas neurogenic tumours and myelolipomas are characteristic findings in the posterior compartment. Vascular tumours, lipomas, adenomatoid tumours, Castleman disease, or mediastinitis are further examples of less frequent tumours or tumorous lesions affecting the mediastinum. This review focuses on benign mediastinal lesions with an emphasis on benign tumours of the thymus. Besides histology, characteristic epidemiological and clinical aspects prerequisite for the correct diagnosis and patient management are discussed.

On the Histologic Classification of Thymoma

The classification of thymoma continues to be a source of controversy in pathology. The difficulties in histologic classification are evident from the number of proposals that have been offered over the years, as well as for the continuous changes and modifications introduced by the World Health Organization to their classification system over the past 20 years. We analyze here some of the issues involved in the classification of these tumors and the difficulties encountered for practicing pathologists in deciphering the "letters and numbers" system devised by the World Health Organization. We would like to propose an alternate approach to thymoma histologic classification that capitalizes on the basic observation of their cytologic features and incorporates the pattern of growth resulting from the interplay of the tumor cells with other cellular constituents as a secondary characteristic. The proposed histologic classification provides a simplified, reproducible means of histologically categorizing these tumors and can be easily understood by most practicing pathologists in simple and clear morphologic terms.

Small molecule multitarget antiangiogenic inhibitor treatments for advanced thymic epithelial tumors: A retrospective study

BACKGROUND

Thymic epithelial tumors (TETs) are rare malignant tumors with limited treatment options. No established second-line treatment regimen is available following the preferred first-line chemotherapy, resulting in unsatisfactory efficacy and poor prognosis for patients with advanced TETs. This study aimed to evaluate the efficacy of small molecule multitarget antiangiogenic inhibitors as well as the prognostic factors for advanced TETs.

METHODS

A retrospective study was conducted using data from a real-world database. Clinical information and survival follow-up data were collected from 52 patients with advanced TETs who received small molecule multitarget antiangiogenic inhibitors at Zhejiang Cancer Hospital between August 10, 2016 and August 10, 2022. The short-term efficacy of the treatments, survival time of the patients, and relevant prognostic factors of advanced TETs were analyzed.

RESULTS

Out of the 52 patients included in this study, 16 had thymoma and 36 had thymic carcinoma. The 52 patients had an overall response rate of 21.1% and a disease control rate of 94.2%. In addition, the median progression-free survival (PFS) was 8.05 months, and the overall survival (OS) was 25.00 months. Apatinib was given to 33 patients, anlotinib to 15 patients, and sunitinib or lenvatinib to four patients. Only seven patients received antiangiogenic inhibitors as their first-line therapy, 27 patients as their second-line therapy, and 18 patients as third-line or subsequent therapy. Meanwhile, 42 patients received monotherapy with an antiangiogenesis inhibitor, while 10 patients received combination therapy. Univariate analysis indicated that the combined treatment was associated with a superior OS (p = 0.044); multivariate analysis indicated that the combined treatment was an independent prognostic factor for PFS (p = 0.014) and OS (p = 0.012).

CONCLUSION

The findings suggest that small molecule multitarget antiangiogenic inhibitors are efficacious as second or post-line treatments as a viable alternative treatment option for patients with advanced TETs.

Diagnostic utility of LMO2 immunohistochemistry in distinguishing T-lymphoblastic leukemia/lymphoma from thymoma

Distinguishing T-lymphoblastic leukemia/lymphoma (T-ALL/T-LBL) from thymomas (especially B1 or B2 type) can be challenging particularly in limited trucut biopsy material where appreciating architecture is difficult or the background epithelial component does not provide tangible evidence for definite diagnosis. As a pathologist, it is important to accurately diagnose these neoplasms because they have entirely distinct management protocols. Recent studies have reported that LIM Domain Only 2 (LMO2) is expressed in neoplastic lymphoblasts of T-ALL/T-LBL and is absent in thymocytes of normal thymuses or thymomas. An observational study was done to test the sensitivity and specificity of LMO2 in differentiating neoplastic lymphoblasts from thymocytes of thymomas/normal thymuses. Our study showed that LMO2 had sensitivity of 70% and specificity of 100% in diagnosing LBL. None of the thymomas (B1 or B2 type) showed expression of LMO2 in the neoplastic cells. LMO2 is a reliable marker of transformed T-cell precursors and should be routinely included in immunohistochemical panel when evaluating thymic/mediastinal neoplasms.

The International Association for the Study of Lung Cancer Thymic Epithelial Tumors Staging Project: Proposals for the N and the M Components for the Forthcoming (Ninth) Edition of the TNM Classification of Malignant Tumors

INTRODUCTION

Stage classification is an important underpinning of management in patients with cancer and rests on a combination of three components-T for tumor extent, N for nodal involvement, and M for distant metastases. This article details the revision of the N and the M components of thymic epithelial tumors for the ninth edition of the TNM classification of malignant tumors proposed by the Thymic Domain of the International Association for the Study of Lung Cancer Staging and Prognostic Factors Committee.

METHODS

The N and M components of the eighth edition staging system were verified by a large international collaborative data source through a data-driven analysis. A total of 9147 cases were included for analysis, including 7662 thymomas, 1345 thymic carcinomas, and 140 neuroendocrine thymic tumors.

RESULTS

Lymph node involvement rates were 1.5% in thymomas and 17.6% and 27.7% in thymic carcinomas and neuroendocrine thymic tumors, respectively. Rates of lymph node metastasis were increasingly higher in tumors with higher T stage and higher-grade histologic type. Survival analysis validated the differences in the N and M categories proposed in the eighth edition staging system. Good discrimination in overall survival was detected among pathologic (p)N and pM categories in patients with thymoma and thymic carcinoma.

CONCLUSIONS

No changes are proposed from the eighth edition for the N and M components. The proposed stage classification will provide a useful tool for management of the disease among the global thymic community.

WHO histological classification and tumor size are predictors of the locally aggressive behavior of thymic epithelial tumors

OBJECTIVE

The aim of this study was to explore the influencing factors that affect the local invasive behavior of thymic epithelial tumors (TETs).

METHOD

We retrospectively analyzed 524 patients with TETs who underwent surgical treatment at our center from January 2010 to January 2022. Cox regression analysis was applied to identify predictors associated with the prognosis of TET. Logistic regression analysis was used to analyze the factors associated with the locally invasive behavior of TETs. Receiver operating characteristic analysis and the Youden index were applied to determine the predictive efficiency and cutoff value.

RESULTS

There were 275 males and 249 females with a median age of 56 years. Seventy-seven patients had locally invasive behavior. The prognosis of local invasive TETs was significantly worse that of noninvasive TETs (P < 0.001). WHO classification and tumor size were two hazard factors for tumor invasive behavior. The risk of local invasion increased by 2.196 (OR (95 % CI): 1.813-2.659) times for each grade in WHO classification with a change from type A to thymic carcinoma. The tumor size cutoff of 6 cm represented a distinct boundary in predicting the hazard of local invasion (AUC: 0.784, specificity: 0.711, sensitivity: 0.726).

CONCLUSION

WHO classification and tumor size are important factors in predicting the locally aggressive behavior of TETs. The invasion capability of TETs is constantly increasing with an escalation in WHO classification. Tumors greater than 6 cm in size have a higher risk for local invasion.

An Overview of the Use of Anti-Angiogenic Agents in the Treatment of Thymic Epithelial Tumors

Angiogenesis significantly influences the carcinogenesis of thymic epithelial tumors (TET). Both thymomas and thymic carcinoma (TC) overexpress VEGF-A and VEGFR-1 and -2. This review aims to provide an appraisal of the use of anti-angiogenics in the treatment of TET. The literature research identified 16 studies that were deemed eligible for further analysis. Seven studies assessed the clinical efficacy of sunitinib and five studies the use of apatinib and/or anlotinib. The multicenter Japanese phase II REMORA trial investigated the efficacy of lenvatinib, which is a multi-targeted inhibitor of VEGFR, FGFR, RET, c-Kit, and other kinases. The objective response rate was 38% (25.6-52%), which is the highest documented in TET that progressed after first-line chemotherapy. Anti-angiogenic agents may be useful in the treatment of TET, which are not amenable to curative treatment. Their toxicity profile seems to be acceptable. However, angiogenesis inhibitors do not appear to have a major influence on either thymomas or TC, although multikinase inhibitors may have some effect on TC. The current evidence suggests that the most active agent is lenvatinib, whereas sunitinib could be proposed as an acceptable second-line therapy for TC. Further research concerning the combination of immune checkpoint inhibitors with anti-angiogenic drugs is warranted.

PAX1 expression in thymic epithelial neoplasms and morphologic mimics

Thymic epithelial neoplasms are morphologically diverse and can pose a diagnostic challenge that is complicated by a lack of immunohistochemistry (IHC) markers that are entirely sensitive and specific for thymic epithelium. Polyclonal PAX8 is often used in this context, but it is not a specific marker. The PAX1 transcription factor shares significant homology with PAX8 and plays an integral role in thymic development in humans and murine models. This study evaluated the role of PAX1 IHC in differentiating thymic epithelial neoplasms from morphologic mimics on whole slide tissue sections. The PAX1 antibody stained all 74 thymoma cases; however, there was wide variability in staining intensity within each subtype. The antibody was less sensitive in thymic carcinomas and thymic neuroendocrine tumors compared to thymomas and demonstrated weak staining in a subset of morphologic mimics (21 squamous cell carcinomas, 6 pulmonary neuroendocrine tumors, 1 mesothelioma, 1 lymphoblastic lymphoma, and 1 granulosa cell tumor). With a H-score positive threshold of 75, the antibody had 100% specificity, and sensitivities of 92%, 56%, and 47% in thymomas, thymic neuroendocrine tumors, and thymic carcinomas respectively. The PAX1 antibody showed frequent geographic reduction in staining consistent with compromised antigenicity from variable formalin fixation. PAX1 IHC has a moderate-to-high sensitivity for thymic epithelial neoplasms; however, the wide staining variability and fixation effects may lead to difficulty with consistent interpretation. This marker is unlikely to supplant the role of PAX8 in diagnostic practice, but it may be a useful addition to immunohistochemistry panels when evaluating for thymic primary tumors.

Good's syndrome: brief overview of an enigmatic immune deficiency

Good's syndrome, an infrequent adult-onset immunodeficiency is characterized by the triad of thymoma, hypogammaglobulinemia, and increased susceptibility to recurrent infections. The clinical presentation is highly variable, with a spectrum ranging from recurrent bacterial and opportunistic infections to concomitant autoimmune diseases and, sometimes malignant pathologies. Due to heterogeneous clinical phenotypes and the lack of adequate diagnostic criteria, its recognition is often challenging, even delaying it by years. It is one of the most unusual, less studied form of the immune deficiency syndromes with a still unknown pathophysiology. It was initially considered a thymoma-associated variant of primary antibody deficiencies with a reduced or absent number of mature B cells, but it later emerged that significant defects of T cell-mediated immune functions are the underlying cause of opportunistic infections. On the basis of current evidence, Good's syndrome is evaluated as a distinct acquired form of combined immunodeficiency states and classified as a phenocopy of primary immunodeficiency diseases. Epigenetic and acquired genetic factors can play an ultimate role in its evolution.

Thymic epithelial tumour radiotherapy in the UK: A survey of current clinical practice

Significant variation in treatment centre setup and radiotherapy practice for thymic epithelial tumours (TET) was identified through a comprehensive survey of current UK Clinical (Radiation) Oncology practice. Multi-centre collaboration and wider TET specific multidisciplinary team meetings are needed and will be essential for developing expertise in TET radiotherapy.

The International Association for the Study of Lung Cancer Thymic Epithelial Tumor Staging Project: A Re-Assessment of the International Thymic Malignancy Interest Group/International Association for the Study of Lung Cancer Lymph Node Map for Thymic Epithelial Tumors for the Forthcoming Ninth Edition of the TNM Classification of Malignant Tumors

INTRODUCTION

A lymph node map is the pillar on which accurate assignment and documentation of nodal classification stands. The International Thymic Malignancy Interest Group created the first map for thymic epithelial malignancies in conjunction with the eighth edition of the TNM classification, representing the first official TNM classification of thymic epithelial malignancies. The map was based on clinical experience and published studies, but it was largely empirical because of limited available data. Dissemination of the map and implementation of a standard thymic stage classification across the world in 2017 have provided more consistent and granular data.

METHODS

More than twice as many cases of node involvement are available for analysis in the current database compared with that of the eighth edition database, allowing validation of many aspects of the eighth edition map. This article details the process and considerations for refinement of the thymic map for the ninth TNM used by the Thymic Domain of the Staging and Prognostic Factors Committee of the International Association for the Study of Lung Cancer. The committee evaluated a large international collaborative data set, published anatomical and clinical studies pertaining to lymph node spread from thymic epithelial tumors, in conjunction with the analysis underlying refinements of the TNM components for the ninth edition TNM classification.

RESULTS

The node map boundaries of the N1 and N2 categories remain unchanged. Visual clarifications have been added to the nomenclature of nodal stations within these regions.

CONCLUSIONS

On the basis of the recommendation to keep the N component unchanged for the ninth edition TNM classification, the lymph node map remains unchanged as well; however, clarifications have been added to facilitate clinical use.

The International Association for the Study of Lung Cancer Thymic Epithelial Tumors Staging Project: Proposal for a Stage Classification for the Forthcoming (Ninth) Edition of the TNM Classification of Malignant Tumors

INTRODUCTION

A TNM-based system for all types of thymic epithelial tumors was introduced in the eighth edition of the TNM classification of thoracic malignancies. The Thymic Domain of the Staging and Prognostic Factors Committee of the International Association for the Study of Lung Cancer, composed of multispecialty international experts, was charged to develop proposals for the ninth edition. This article outlines the proposed definitions for the T, the N, and the M components and their combination into stage groups.

METHODS

A large central database of 11,347 patients with thymic epithelial tumors was assembled thanks to the contribution of the major thymic organizations worldwide and analyses were carried out for the T, the N, and the M components and the stage groups. Overall survival was the outcome measure for patients with completely and incompletely resected tumors, and recurrence for those with complete resection. When the number of patients was sufficient, analyses were performed separately for thymomas, thymic carcinomas, and neuroendocrine thymic tumors.

RESULTS

Tumor size is included in the T1 category as T1a (≤5cm) and T1b (>5 cm); the mediastinal pleura is dropped as a T descriptor; invasion of the lung or phrenic nerve is reclassified as T2 (instead of T3). No changes are proposed for the N and the M components from the eighth edition. The stage groups remain the same.

CONCLUSIONS

The proposed changes for the ninth edition of the TNM classification set the stage for further progress in the future for these rare tumors.