Reported herein is an extremely rare case of primary pulmonary myxoid sarcoma (PPMS). A 31-year-old man presented with a 2.7 cm-sized pulmonary tumor surrounded by capsule-like fibrosis. The patient has been free of disease for 5.8 years after surgery. This tumor focally showed endobronchial features, and consisted of reticular cords of oval, short spindle, or polygonal cells with swollen vesicular nuclei accompanied by an abundant myxoid stroma, closely resembling extraskeletal myxoid chondrosarcoma. Tumor cells were diffusely positive for vimentin and focally positive for epithelial membrane antigen, but were negative for cytokeratin, TTF-1, Napsin A, S-100 protein, CD34, desmin, smooth-muscle actin, CD10, p63, calponin, h-caldesmon, c-kit, HMB-45, synaptophysin, or glial fibrillary acid protein. Our reverse transcription-polymerase chain reaction using the formalin-fixed, paraffin-embedded tumor tissues detected EWSR1-CREB1 fusion transcript, but could not demonstrate EWSR1-ATF1 fusion or EWSR1/TAF15/TFG-NR4A3 fusion. These findings indicate that the current tumor is an additional case of PPMS with EESR1-CREB1 fusion, recently reported by Thway et al. Some cases of PPMS can behave in an indolent manner.

We report a case of a 67-year-old woman with an invasive ciliated muconodular papillary tumor (CMPT) that developed in her right middle lobe. The current tumor was incidentally detected during a follow-up imaging examination for a large cell carcinoma that was resected 10 years previously. Partial removal of the middle lobe showed a 2 cm-sized, solid and myxoid tumor located in the peripheral region. Histologically, this tumor primarily consisted of ciliated columnar cells, mucous cells, and basal cells, all of which had relatively swollen nuclei and were proliferating in a lepidic or papillary/micropapillary manner. These features were consistent with those of previously reported CMPT. In addition, atypical spindle tumor cells with more swollen nuclei, which were partly continuous to less atypical basal tumor cells, were focally found and invaded fibrous stroma in a reticular fashion. Immunohistochemically, both basal cells and atypical spindle tumor cells were positive for pancytokeratin, cytokeratin 5/6, and p40. Increased p53 positivity was found in these invading spindle cells compared with basal tumor cells. Neither BRAF V600E nor V600K mutation was detected. We concluded that this tumor was an extremely rare invasive case of CMPT, possibly representing malignant transformation of basal tumor cell components of CMPT.

CK7 + CHs occur relatively frequently in non-neoplastic liver disease, associated with centrilobular scarring and the presence of CK7-positive periportal hepatocytes, and appear to be a non-specific phenomenon with respect aetiology of underlying disease. CK7 + CHs may represent age-dependent activation of hepatic progenitor cells or a regenerative phenomenon of hepatocytes themselves, both of which might contribute to liver regeneration.

Peritoneal seeding (PS) of hepatocellular carcinoma (HCC) is uncommon, and the clinicopathological features are poorly understood. A total of 181 autopsy cases of HCC, including 171 cases with detailed clinical information, was investigated for PS and evaluated. PS was identified in 17 cases (9.4%), and was locally (70.6%) or entirely (29.4%) distributed in the peritoneal cavity, involving the diaphragm (76.5%), omentum (47.1%), or alimentary tract serosa (47.1%). Compared with primary HCC, PS showed similar or slightly undifferentiated features (88.2%) and exhibited more differentiated features (11.8%). In 15 cases (88.2%) of HCC with PS, primary HCC showed membranous β-catenin immunoreactivity. However, in five cases (33.3%), respective PS lost this immunoreactivity. PS was significantly associated with rupture of HCC (P= 0.012), direct diaphragmatic invasion (P= 0.001), and lymph node metastasis (P < 0.001), indicating these are high risk factors for PS; there was no significant association with a past history of percutaneous fine-needle biopsy, percutaneous ethanol injection and/or radiofrequency ablation (P= 0.97), or metastasis to lung (P= 0.13), bone (P= 0.71), or adrenal gland (P= 0.79). PS can infrequently proliferate aggressively with more differentiated features. Loss of membranous β-catenin expression may be associated with PS of HCC.

Ectopic hamartomatous thymoma (EHT) is a rare benign neoplasm of the lower neck suggesting branchial origin. Despite use of the term thymoma in the nomenclature, there is no evidence of thymic origin or differentiation. It affects middle-aged adults with a remarkable male predominance. To date less than 80 cases have been reported in the English literature. We present here two additional cases of EHT. The first is a benign case in a 31-year-old man, showing typical histological features. The second is a malignant case in a 70-year-old woman, showing intraductal carcinoma arising in intimate association with an EHT. These cases are presented in the context of a review of cases reported in the English literature. The exact origin has not been identified, but is considered to be of branchial apparatus, creating a quandary about the best terminology. Recently, the designation "branchial anlage mixed tumor" or "thymic anlage tumor" were proposed, but do not quite reflect the true nature of the neoplasm. To avoid taxonomic confusion, international consensus on terminology is desired. As this entity is a neoplasm that shows dual mesoderm and endoderm derivation/differentiation, we propose a new name "biphenotypic branchioma."