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Rationale Pulmonary artery intimal sarcoma is a rare tumor with exceptionally high mortality and easily misdiagnosed as pulmonary thromboembolism pulmonary thromboembolism (PTE) due to the nonspecific clinical presentation and symptom. Misdiagnosis or untimely diagnosis makes the disease progress to an advanced stage and eventually leads to a poor prognosis. Patient concerns A 37-year-old Chinese female presented with chest tightness and dyspnea for 3 months. Echocardiography and chest computed tomography revealed an intraluminal obstruction of the pulmonary arteries. Tests of serum tumor makers showed slight elevation for carbohydrate antigen-125, and α-fetoprotein. PTE was suspected according to the radiological and laboratory findings. Diagnosis Microscopic findings of the presumed thrombus showed prominent myxoid and edematous background with atypical spindled cells and curvilinear vascularity. Immunohistochemical staining demonstrated that the atypical spindled cells were positive for vimentin but negative for CK, S100, SMA, desmin, CD68, STAT6, CD34, β-catenin, ALK-p80, p53, and MDM2. According to the radiological and pathological findings, the diagnosis of fibrosarcoma of pulmonary artery was made. Interventions The patient underwent surgical resection and the mass was excised as completely as possible. Outcome Follow-up information showed no evidence of recurrence or metastasis after 3 months postresection. Lessons Because of the low incidence rate, nonspecific clinical symptoms, and radiological findings, primary fibrosarcoma of the pulmonary artery is commonly misdiagnosed as PTE. Pathological examination is necessary to confirm the diagnosis.

Rationale: Primary testicular natural killer (NK)/T-cell lymphoma is an extremely rare and highly aggressive lymphoid malignancy. At present, only 20 cases have been reported. Patient concerns: A 32-year-old Chinese man complained of discomfort and swelling of his right testicle for 3 months. Physical examination revealed a 10 × 10 × 9.5 cm mass on the right side of the scrotum area. Diagnoses: Pathologic evaluation showed effacement of normal testicular parenchymal architecture by small-to-medium-sized lymphoid cells with irregular nuclear profiles, and immunohistochemical studies positively expressed CD2, CD56, cytoplasmic CD3, granzyme B, perforin, and TIA-1. Therefore, the patient was diagnosed with primary testicular NK/T-cell lymphoma. Interventions: The patient underwent CHOP (cyclophosphamide (CTX), pirarubicin (THP-ADM), vincristine (VCR), and prednisolone (PDN)) chemotherapy. Outcomes: The patient relapsed 5 months after his initial presentation and died after an infection and gastrointestinal bleed. Lessons: Clinicopathological assessment of this rare case highlights the clinical and pathological features required to diagnose testicular NK/T-cell lymphoma. In addition, it highlights the dismal survival of these patients. We hope it may serve as a reference aiding prompt clinical diagnosis, which can hopefully improve the survival and quality of life of these patients.

Rationale Signet-ring cell is a rare morphological finding in bone marrow, which usually indicates metastatic carcinoma from either the gastrointestinal tract or a primary hematolymphoid neoplasm. Here, we present a very unusual case of lobular breast carcinoma with metastasis to the bone marrow. Patient concerns A 67-year-old female with estrogen receptor (ER)-positive lobular breast carcinoma was staged as T3N3M0, and treated with modified radical mastectomy followed by chemotherapy and radiotherapy. One year after treatment, she was noted to have moderate thrombocytopenia on complete blood count with the remainder of the parameters within normal limits. Radiographic examination revealed no evidence of recurrent disease. Diagnosis Bone marrow biopsy was performed to exclude therapy-related myelodysplastic syndrome (MDS), which demonstrated hypercellularity with "hyperplastic" hematopoiesis. Upon closer inspection, a few signet-ring cells were identified which morphologically resembled histiocytes. These formed an interstitial infiltrate among the predominantly hematopoietic elements, and could have been easily overlooked. Immunohistochemistry demonstrated that these signet-ring cells were positive for pancytokeratin as well as ER which confirmed metastatic lobular breast carcinoma. On retrospective review of the aspirate smear, rare signet-ring cells were identified. Interventions The patient was treated with additional chemotherapy. Outcomes The patient eventually succumbed to overt dissemination after 14 months. Lessons Due to the relative discohesiveness of lobular breast carcinoma, the cells frequently assume single-cell infiltration in bone marrow. This attribute, along with small cell size, bland cytologic features and paucity of tissue response, contributes to its escaping from identification on hematoxylin-eosin (H&E) sections. In this case, the signet-ring cells were hidden in apparently hyperplastic hematopoiesis. Careful inspection raised the possibility of occult metastasis which was readily detected and confirmed with immunohistochemistry.

RATIONALE Primary central nervous system lymphoma (PCNSL) is a rare form of non-Hodgkin lymphoma with a dismal outcome. Most patients relapse in intracranial sites and

Rationale:Primary central nervous system histiocytic sarcoma (PCNSHS) is a rare lymphohematopoietic tumor with a histiocytic cell origin. To our knowledge, only 28 cases have been published in English and 2 cases in Chinese.Patient concerns:A 49-year-old Asian female presented to the hospita

Rationale Primary thyroid-like low-grade nasopharyngeal papillary adenocarcinoma (TL-LGNPPA) is an extremely rare malignant nasopharyngeal tumor with features resembling papillary thyroid carcinoma including nuclear positive expression of thyroid transcription factor-1 (TTF-1). Patient concerns A 64-year-old male presented with nasal bleeding and a foreign body sensation of the nasopharynx. Laryngoscopy revealed a 2.0-cm broad-based mass with a smooth surface on the posterior wall of the nasopharynx. A biopsy was obtained. Diagnoses Histopathologic examination demonstrated tumor cells arranged in both papillary and glandular architecture. The tumor cells express nuclear immunoreactivity for TTF-1. The diagnosis of TL-LGNPPA was made. Interventions After the patient was diagnosed with TL-LGNPPA, he underwent complete surgical resection. Outcomes There was no recurrence or evidence of metastatic disease at the 12-month follow-up. Lessons TL-LGNPPA is easy to misdiagnose as metastatic papillary thyroid carcinoma or other relative primary adenocarcinomas. It is important to have a broad differential diagnosis and know the key features of each entity because the prognosis and clinical treatment of each may differ.