SEOM-GECOD clinical guideline for unknown primary cancer (2021)

Cancer of unknown primary site (CUP) is defined as a heterogeneous group of tumors that appear as metastases, and of which standard diagnostic work-up fails to identify the origin. It is considered a separate entity with a specific biology, and nowadays molecular characteristics and the determination of actionable mutations may be important in a significant group of patients. In this guide, we summarize the diagnostic, therapeutic, and possible new developments in molecular medicine that may help us in the management of this unique disease entity.

Clinical Impact of F-18 FDG PET-CT on Biopsy Site Selection in Patients with Suspected Bone Metastasis of Unknown Primary Site

Purpose

We investigated the clinical role of F-18 fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) in the identification of the primary site and the selection of the optimal biopsy site in patients with suspected bone metastasis of unknown primary site.

Methods

The patients with suspected bone metastasis who underwent PET-CT for evaluation of primary site were enrolled in this study. The primary sites were identified by the histopathologic or imaging studies and were classified according to the FDG uptake positivity of the primary site. To evaluate the guiding capability of PET-CT in biopsy site selection, we statistically analyzed whether the biopsy site could be affected according to the presence of extra-skeletal FDG uptake.

Results

Among 74 enrolled patients, 51 patients had a metastatic bone disease. The primary site was identified in 48 of 51 patients (94.1%). Forty-six patients were eligible to test the association of clinical choice of biopsy site with PET positivity of extra-skeletal lesion. The extra-skeletal biopsies were done in 42 out of 43 patients with positive extra-skeletal uptake lesions. Bone biopsies were inevitably performed in the other three patients without extra-skeletal uptake lesions. The association came out to be significant (Fisher's exact test, P < 0.001).

Conclusion

F-18 FDG PET-CT significantly contributed not only to identify the primary site but also to suggest optimal biopsy sites in patients with suspected bone metastasis.

Lymph node cancer of the mediastinum with a putative necrotic primary lesion in the lung: a case report

Background

Although mediastinal lymph node cancer is presumed to originate in the lung, the primary site is usually unidentified, so the pathological course remains unclear. We recently encountered a case of mediastinal lymph node cancer having a putative primary lesion remaining in the lung as a necrotic focus.

Case presentation

The patient was a 56-year-old man who visited our department because computed tomography screening had revealed a nodular shadow in the lingular segment. However, on positron emission tomography, fluorine-18 deoxyglucose accumulation was detected in a subcarinal lymph node and not in the nodule in the lingular segment. Biopsy of the lung tumor and the lymph node was performed via minimal thoracotomy. Intraoperative pathologic examination showed necrosis alone and no malignant findings in the lung tumor. By contrast, carcinoma was detected in the lymph node. Additional subcarinal lymph node dissection was performed. Results of postoperative histopathologic examination indicated poorly differentiated adenocarcinoma of the subcarinal lymph node. Meanwhile, the nodule in the lingular segment was speculated to be a spontaneously resolved primary focus of lung cancer.

Conclusions

In this case, the primary lung cancer focus resolved spontaneously after lymph node metastasis, explaining the pathogenesis underlying mediastinal lymph node cancer of unknown primary site. For similar cases of malignancy, aggressive treatment, including surgery, is effective.

SEOM clinical guideline on unknown primary cancer (2017)

Cancer of unknown primary site is a histologically confirmed cancer that manifests in advanced stage, with no identifiable primary site following standard diagnostic procedures. Patients are initially categorized based on the findings of the initial biopsy: adenocarcinoma, squamous-cell carcinoma, neuroendocrine carcinoma, and poorly differentiated carcinoma. Appropriate patient management requires understanding several clinical and pathological features that aid in identifying several subsets of patients with more responsive tumors.

Mammary Analogue Secretory Carcinoma Presenting as a Cervical Lymph Node Metastasis of Unknown Primary Site: A Case Report

Background

Mammary analogue secretory carcinoma (MASC) is a pathological entity arising in the salivary glands first described by Skalova et al. [Am J Surg Pathol 2010;34: 599–608]. Here, we report the first case of MASC presenting as a cervical lymph node metastasis of unknown primary site together with a brief review of the literature.

Case Report

We present a 74-year-old male with a painless lump in his left neck. Based on the fine-needle aspiration cytological findings, a possible malignant tumor was suspected. No evidence of a primary lesion was observed using imaging modalities including positron emission tomography/computed tomography. The patient underwent an ipsilateral modified radical neck dissection. Immunohistochemical staining showed that the neoplastic cells were positive for S100 protein and GATA3. A rearrangement of the ETV6 gene was noted during fluorescence in situ hybridization, and the final histopathological diagnosis was MASC.

Conclusion

We encountered a MASC presenting as a cervical lymph node metastasis of unknown primary site. No adjuvant therapy was administered, and no local recurrence or metastatic disease has been detected during a follow-up period of 9 months. This is the first case report of MASC presenting as a cervical lymph node metastasis of unknown primary site and suggests the new properties of MASC.

Merkel cell carcinoma of unknown primary site; case presentation and review of the literature

Merkel cell carcinoma (MCC) is a rare skin malignancy associated with sun exposure and considered as a Neuroendocrine Tumor due to its characteristic histologic features. However there is increasing number of reports of Unknown Primary MCC's (UPMCC). Although initially UPMCC was considered a variant of known primary MCC, there is growing evidence that it could represent a different clinical entity.

We present the case of a 60 year-old male patient who was referred to our department for surgical management of lymph node disease for UPMCC. The patient had undergone excisional biopsy of an inguinal lump, which was found to be an infiltrated lymph node by MCC. The patient underwent full imaging staging including a PET/CT, which failed to identify a primary site, and revealed only intra-abdominal lymph node disease. The patient underwent extended retroperitoneal and inguinal lymph node dissection and remains free of recurrence 16 months postoperatively.

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Unknown Primary Merkel cell carcinoma is a rare NET, which usually presents with extensive lymph node involvement.

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This tumor follows a more indolent natural course than a Merkel cell carcinoma of known primary and of similar staging.

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Surgical excision with R0 resection remains a common practice in the management of unknown primary Merkel cell carcinoma.

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Adjuvant chemotherapy after R0 resection is the usual practice, despite the lack of good quality literature evidence.

[Histological and molecular analysis of brain metastases]

The first step in the diagnosis of a metastatic brain lesion is to exclude a primary central nervous sytem tumour, followed by verification or identification of the primary tumor site, in order to guide the clinician to specific therapy. In addition to morphological features, ancillary immunohistochemical study is most effective for the evaluation of a metastatic neoplasm of unknown primary. Although the main principles are same, there are slight variations in the approach to the secondary lesion in the central nervous system versus other regions. Indeed, immunohistochemical approach focuses on the most common tumor types associated with secondary brain colonization: lung cancer, breast cancer and melanoma. Several studies have reported that targeted therapies are capable of reducing brain metastases in melanoma or non-small cell lung cancer, sometimes with a high dramatic response. These results have clearly impacted routine neuropathological practice. It is likely that molecular subtyping of central nervous system metastases will play an increasing role in the future. In accordance with the recommendations of Inca (French national cancer institute), the pathologist develops appropriate strategies for molecular and immunohistochemical analysis, in order to provide results as soon as possible. This article summarizes the diagnosic approach to brain metastases, with a focus on the recent emergence of targeted therapies.