KRAS mutation-positive mucinous adenocarcinoma originating in the thymus

Lenvatinib-refractory thymic mucinous carcinoma with PIK3CA mutation

Mucinous adenocarcinoma, a very rare type of thymic carcinoma, is aggressive and has a poor prognosis. The optimal treatment for advanced thymic mucinous adenocarcinoma has not yet been established because of its rarity. An oral multi-tyrosine kinase inhibitor, lenvatinib, was approved for treatment of thymic carcinoma in March 2021 in Japan. However, to the best of our knowledge, there are no published reports concerning lenvatinib for thymic mucinous adenocarcinoma. Herein, we report a 39-year-old woman who presented with a 70 mm multilocular cystic tumor in her left anterior mediastinum and a massive pericardial effusion. We diagnosed a Masaoka stage IVb thymic mucinous adenocarcinoma with multiple metastases to the liver and bones, and pericardial dissemination on the basis of the pathologic findings on examination of a video-assisted thoracoscopic tumor biopsy and radiological examinations. She received paclitaxel-carboplatin-based chemotherapy, but developed a left cerebellar metastasis. Second-line chemotherapy with lenvatinib failed to suppress the tumor. She died of cancer progression 5 months after presentation. Here, we report what we believe to be the first case of a thymic mucinous adenocarcinoma treated with lenvatinib. Our patient's thymic mucinous adenocarcinoma was refractory to both cytotoxic chemotherapy and lenvatinib. Using next-generation sequencing, we identified phosphatidylinositol 3-kinase catalytic subunit alpha mutation in the tumor. We suspected an association between this mutation and resistance to lenvatinib. We therefore recommend performing next-generation sequencing when considering introduction of lenvatinib for thymic mucinous adenocarcinoma. A surgical procedure may be necessary for accurate diagnosis and genetic analysis of this histological tumor type.

A primary thymic adenocarcinoma with two components that traced distinct evolutionary trajectories

Even though it is a rare subtype, identifying the genetic features of thymic adenocarcinoma is valuable for a multifaceted understanding of thymic epithelial tumors. We experienced a female patient with thymic adenocarcinoma associated with thymic cysts. The tumor consisted of a solid whitish lesion (lesion-1) and a large cystic lesion with small papillary nodules (lesion-2). Microscopically, lesion-1 exhibited poorly differentiated adenocarcinoma accompanying numerous inflammatory cell infiltrates, and lesion-2 (the nodules within the cystic lesion) exhibited enteric-type adenocarcinoma. Consistent with the histological difference, whole-exome sequencing revealed that these two components exhibited distinct genetic features, except for only a few shared mutations, including CDKN2A truncation. Lesion-1 exhibited microsatellite instability-high signature with high mutation burden, for which immune checkpoint inhibitors might apply; and lesion-2 exhibited whole-genome doubling with KRAS hotspot mutation. Our case presents novel genetic features of thymic adenocarcinoma and demonstrates that distinct mutational processes can be operative within a single tumor.

Primary mucinous adenocarcinoma of the thymus; a rare type of thymic carcinoma. Case Report

Mucinous adenocarcinoma of the thymus is a particularly rare type among thymic carcinomas. Here, we report a patient who underwent complete surgical resection of the primary mucinous adenocarcinoma of the thymus. She was 74 years old and presented with a 60-mm multilocular cystic tumor in her right anterior mediastinum. We performed extended thymo-thymectomy with partial resection of the right upper lobe and pathologically diagnosed the patient with Masaoka stage II mucinous adenocarcinoma of the thymus. Immunohistochemistry showed the absence of PD-L1, suggesting that immune check point inhibitors targeting PD-1/PD-L1 might not be effective in this case. The increased preoperative serum levels of CA19-9 decreased after the operation. CA19-9 is a biomarker for disease status. Future reports should help elucidate the pathogenesis of this disease.

Thymic adenocarcinoma accompanied by type A thymoma and pulmonary minimally invasive adenocarcinoma and harboring distinct gene alterations: A case report

RATIONALE

Thymic adenocarcinoma is an extremely rare thymic carcinoma. The exact genetic alteration associated with thymic adenocarcinoma is unclear. Here, we report a case of thymic adenocarcinoma accompanied by type A thymoma and pulmonary minimally invasive adenocarcinoma (MIA).

PATIENT CONCERNS

A 53-year-old woman presented with multiple nodules in the mediastinum and lung. Thoracic computed tomography revealed nodules in the anterior superior mediastinum and anterior mediastinum near the right pericardium and ground-glass opacity (GGO) in the right superior lobe of the lung.

DIAGNOSIS

The tumor in the anterior superior mediastinum was diagnosed as primary thymic papillary adenocarcinoma. The tumor in the anterior mediastinum near the right pericardium was diagnosed as type A thymoma. The GGO of the right superior lobe of the lung was diagnosed as a MIA.

INTERVENTION

The patient underwent thoracoscopic mediastinal tumor resection and partial lobectomy in our hospital.

OUTCOMES

The postoperative course was uneventful. The patient is alive and free of the disease for 22 months after diagnosis.

LESSONS

Thyroid transcription factor 1 (TTF-1) was positive in this case of thymic adenocarcinoma, which indicated that a thymic adenocarcinoma with TTF-1-positive may not necessarily be a metastasis of lung or thyroid adenocarcinoma. The positive staining of CD5 and CD117 can help us to confirm the thymic origin. Molecular genetic analysis indicated that these tumors harbored different mutations. The thymic adenocarcinoma and type A thymoma both had the mutation of KMT2A, but the mutation sites were different. KMT2A mutation may be a common genetic change in thymic tumorigenesis. The genetic alterations disclosed in this study will help expand the understanding of thymic tumors.

Common and rare carcinomas of the thymus

Thymic carcinoma encompasses a diverse group of rare tumors that occur almost exclusively in the prevascular (anterior) mediastinum. Thymic carcinomas have a worse outcome than thymomas with a median time to death of under 3 years. These tumors lack the typical lobulation of thymomas, exhibit commonly more cytologic atypia, are associated with a desmoplastic stromal reaction, and lack thymocytes, features that distinguish them from thymomas. The most common thymic carcinoma is squamous cell carcinoma; other subtypes include mucoepidermoid carcinoma, NUT carcinoma, and adenocarcinoma, among others. Largely due to multi-institutional and global efforts and meta-analysis of case reports and series, some of the thymic carcinoma subtypes have been studied in more detail and molecular studies have also been performed. Morphology and immunophenotype for the vast majority of thymic carcinoma subtypes are similar to their counterparts in other organs. Therefore, the distinction between thymic carcinoma and metastatic disease, which is relatively common in the prevascular mediastinum, can be challenging and in general requires clinical and radiologic correlation. Although surgical resection is the treatment of choice, only 46 to 68% of patients with thymic carcinoma can undergo resection as many other tumors present at high stage with infiltration into vital neighboring organs. These patients are usually treated with chemotherapy and/or radiation. The search for better biomarkers for prognosis and treatment of thymic carcinomas is important for improved management of these patients and possible targeted therapy.