Presented are three casuistics of seemingly identical breast lesions which even by adopting advanced laboratory techniques may represent diagnostic challenge. Microscopic features of some bland spindle cell lesions of different histogenesis (epithelial or mesenchymal) are misleading and a potential source of unaware errors, which might affect optimal therapeutic strategy. In the setting of three diverse entities (low-grade spindle cell metaplastic carcinoma, desmoid fibromatosis and phyllodes tumor) is documented both demanding diagnostic algorithm and revealing molecular landscape on one side as well as evolving predictive/prognostic parameters on the other one. Close interdisciplinary cooperation is inevitable for accurate interpretation/understanding of revealed diagnostic facts which is required for adjustment of competent rational and individualized therapy.

Invasive lobular carcinoma (ILC) is the most common special type of invasive breast cancer (IBC), accounting for 5-15% of IBCs. The distinct histomorphology of ILC reflects a special tumor biology, the hallmark of which is the lack of E-cadherin expression. However, the occasional presence of E-cadherin expression and the presence of IBC of no special type (IBC, NST)-like morphologies in ILC and vice versa make the diagnosis challenging.  We present two cases of the alveolar variant of ILC, a diagnostically challenging entity. The first case is an 81-year-old female with two discrete right breast masses at 1 o\'clock and 9 o\'clock positions.  The second case is a 61-year-old female with two discrete left breast masses located at 11 o\'clock and 12 o\'clock positions. Core needle biopsies and subsequent mastectomy were performed in both cases. On histology, three tumor foci were identified in the first case. The 1 o\'clock focus showed IBC, NST, grade 3/3, ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). The 9 o\'clock focus revealed ILC, classic and alveolar variants, grade 2/3, while a nearby third incidental focus was ILC, alveolar variant, both supported by lack of E-cadherin and β-catenin immunostaining.  The second case showed ILC, alveolar variant, grade 1 with LCIS component in the 11 o\'clock lesion on both biopsy and mastectomy specimens. The lesion at the 12 o\'clock position was diagnosed as IBC, NST, grade 2 with high-grade DCIS and LCIS components.  It is challenging to distinguish the alveolar variant of ILC from IBC, NST, and in situ lesions because of the overlapping morphology and occasional E-cadherin expression. Altered adherence of lobular cells may also be due to loss of α-, β-, and γ-catenins, and cytoplasmic re-localization of p120-catenin. Therefore, in ILC, the lack of β-catenin can be used as an adjunct along with E-cadherin. Myoepithelial markers such as p63 and smooth muscle myosin heavy chain (SMMHC) can be used to distinguish the alveolar variant of ILC from LCIS.

Desmoid tumors are locally aggressive, benign neoplasms originating in connective tissues. Although the exact pathophysiology remains unknown, antecedent trauma or surgery are believed to be important contributing factors. The occurrence of paraspinal desmoid tumor in pediatric patients is extremely uncommon. Here, we present an exceedingly rare case of a pediatric patient with no surgical or family history who developed a paraspinal desmoid tumor. A 9-year-old female patient presented with 4 months of progressive back pain, right lower extremity weakness, and numbness. Spinal imaging revealed a left epidural paraspinal mass compressing her thoracic spinal cord and extending into the left thoracic cavity. A multidisciplinary approach with neurosurgery and thoracic surgery enabled gross total resection of the lesion. The patient had complete resolution of her symptoms with no signs of residual tumor on postoperative imaging. Pathology revealed a desmoid tumor that avidly stained for beta-catenin. On her last follow-up, she developed a recurrence, to which she was started on sorafenib therapy. Desmoid tumors are rare connective tissue neoplasms that often occur after local tissue trauma, such as that caused by surgery. This report presents a rare case of a pediatric paraspinal desmoid tumor that occurred in a patient with no surgical or family history. Such tumors should undergo surgical resection for symptomatic relief and tissue diagnosis. Close clinical and radiographic surveillance are essential in these patients due to the high recurrence rates of desmoid tumor.

Most cases of desmoid-type fibromatosis (DTF) exhibit a mutation in APC or CTNNB1. We report a case of mesenteric DTF in which no mutation in APC or CTNNB1 was found, but a germline variant of uncertain significance (VUS) in RAD51C and a subclonal mutation in MYST3 were identified. Whether these genetic changes are important in DTF in this case, or whether genetically conventional DTF cells were present at a density below detection is unknown; it will be of interest to see results in further studies of wild-type APC/CTNNB1 cases.

Multifocal desmoid-type fibromatosis (DTF) is very rare and usually regional. We report three cases that initially appeared to be multifocal, but subsequent detailed imaging revealed unsuspected tracking along nerves in two cases. This neural spread is reminiscent of neuromuscular choristoma (NMC), a rare developmental lesion in which mature skeletal muscle cells, or rarely smooth muscle cells, infiltrate and enlarge peripheral nerves. NMC is frequently associated with DTF. These two cases suggest that DTF spread along nerves and appeared as distinct multifocal lesions while actually being contiguous. The third case was felt to represent true multifocal tumor development, possibly due to tumor seeding at the time of chest surgery. The relationship of DTF to NMC is discussed.

Ameloblastic carcinoma is a rare malignant neoplasm with characteristic histopathological features that are directed towards an aggressive surgical approach than benign odontogenic lesions. It affects people of all ages, mostly in the posterior mandible, without a preference for race or gender. De novo cancer is one of its primary types, while the second type is defined as a malignant change from an antecedent case of benign ameloblastoma. The rapid progression of molecular biology led to the revelation that ameloblastoma contains a BRAF-V600E genetic mutation over 60%. Besides conventional ameloblastic carcinomas, rare histologic variants have also been described in the literature, including clear and spindle cells. These variants pose diagnostic challenges as to whether it is a dedifferentiation or a distinct entity. The dearth of data lends credence to the notion that these histologic variations are related to high-grade neoplasms and more aggressive outcomes. As a result, the current report intends to analyze a series of patients diagnosed with conventional ameloblastic carcinoma of the head and neck region with spindle and clear cell types along with a brief assessment of the literature.

OBJECTIVE: Cancer/testis antigens (CTAs) are well-known molecular targets with expression restricted to testicular germ cells and malignant tumors. T-cell receptor (TCR)-engineered T-cell (TCR-T) therapy against CTAs in patients with sarcoma has shown substantial progress, but resistance to TCR-T therapy remains a critical problem. In this report, we present a case of synovial sarcoma treated with TCR-T therapy targeting the New York-esophageal squamous cell carcinoma (NY-ESO)-1 protein. Histological findings were compared before and after TCR-T therapy and before and immediately after cryoablation.
METHODS: A 68-year-old man received additional wide resection for synovial sarcoma in the left leg. Due to multiple metastases, he was enrolled in a clinical trial of TCR-T therapy for NY-ESO-1. The tumor demonstrated a 34.9% reduction in diameter. However, disease progression occurred by day 84 after TCR-T therapy. Six months after disease progression, cryoablation was performed for right posterior rib lesion and tumor specimens were obtained by needle biopsy both before and immediately after cryoablation. Ten months after the diagnosis of disease progression, the patient died. Expression levels of NY-ESO-1, human leukocyte antigen, and immune checkpoint proteins remained unchanged before and after TCR-T therapy. Beta catenin was up-regulated in recurrent tumor tissues after TCR-T therapy compared to levels observed before TCR-T therapy. Immediately after cryoablation, immunoreactivity for NY-ESO-1 showed a slightly reduction.
CONCLUSIONS: Up-regulation of beta-catenin in synovial sarcoma with recurrence after TCR-T therapy may be involved in T-cell exclusion and resistance to TCR-T therapy. Needle biopsy after cryoablation can be performed with sufficient pathological diagnostic accuracy including immunostaining.

BACKGROUND: Hematogenous tumor spread of malignant meningiomas occurs very rarely but is associated with very poor prognosis.
METHODS: We report an unusual case of a patient with a malignant meningioma who developed multiple metastases in bones, lungs and liver after initial complete resection of the primary tumor. After partial hepatic resection, specimens were histologically analyzed, and a complete loss of E-cadherin adhesion molecules was found. No oncogenic target mutations were found. The patient received a combination of conventional radiotherapy and peptide receptor radionuclide therapy (PRRT). Due to aggressive tumor behavior and rapid spread of metastases, the patient deceased after initiation of treatment.
CONCLUSIONS: E-cadherin downregulation is associated with a higher probability of tumor invasion and distant metastasis formation in malignant meningioma. Up to now, the efficacy of systemic therapy, including PRRT, is very limited in malignant meningioma patients.

Mesenteric desmoid-type fibromatosis (DTF) is a rare benign yet aggressive neoplasm that has an unpredictable biological behavior ranging from spontaneous regression to extensive local infiltration and has a high tendency for recurrence. The presenting symptoms are usually nonspecific and mostly related to the large size of the tumor compressing adjacent organs. Imaging studies can be suggestive of the diagnosis, but confirmation is based on histopathological and immunohistochemical examination. The lack of knowledge on the etiology and pathogenetic behavior of this tumor leads to therapeutic and prognostic challenges. Future genetic studies may help in advancing our understanding of this neoplasm and in formulating the proper management and follow-up plan. Here we present a case of a 14-year-old female who presented to the emergency room complaining of diffuse abdominal pain and distention. A computed tomography (CT) scan showed a large mass occupying most of the abdominal cavity and compressing adjacent organs. Exploratory laparotomy with resection and anastomosis was performed, and the histopathological and immunohistochemical examination of the resected mass was consistent with mesenteric DTF.

Intranodal palisaded myofibroblastoma (IPM) is a rare stroma-derived spindle-cell neoplasm of the lymph node with myofibroblastic differentiation and CTNNB1 (β-catenin gene) somatic mutations. We present a case of IPM found incidentally in the staging of lung adenocarcinoma. We describe the major histopathological and phenotypic features, including a palisaded bland spindle cell proliferation with myofibroblastic differentiation and Wnt pathway activation by immunohistochemistry, including β-catenin expression. Production of osteoid-like collagen directly from tumor cells was observed. We confirmed p.Gly34Arg CTNNB1 mutation by direct sequencing. We also reviewed the literature for similar cases.