Despite a standardized diagnostic examination, cancer of unknown primary (CUP) is a rare metastatic malignancy with an unidentified tissue of origin (TOO). Patients diagnosed with CUP are typically treated with empiric chemotherapy, although their prognosis is worse than those with metastatic cancer of a known origin. TOO identification of CUP has been employed in precision medicine, and subsequent site-specific therapy is clinically helpful. For example, molecular profiling, including genomic profiling, gene expression profiling, epigenetics and proteins, has facilitated TOO identification. Moreover, machine learning has improved identification accuracy, and non-invasive methods, such as liquid biopsy and image omics, are gaining momentum. However, the heterogeneity in prediction accuracy, sample requirements and technical fundamentals among the various techniques is noteworthy. Accordingly, we systematically reviewed the development and limitations of novel TOO identification methods, compared their pros and cons and assessed their potential clinical usefulness. Our study may help patients shift from empirical to customized care and improve their prognoses.

Cancer of unknown primary (CUP) is a well-studied entity with guidelines available for the management of patients with CUP. The peritoneum represents one of the metastatic sites in CUP, and peritoneal metastases (PM) could present as CUP. PM of unknown origin remains a poorly studied clinical entity. There is only one series of 15 cases, one population-based study, and few other case reports on this subject. Studies on CUP, in general, cover some common tumour histological types like adenocarcinomas and squamous carcinomas. Some of these tumours may have a good prognosis though majority have high-grade disease with a poor long-term outcome. Some of the histological tumour types commonly seen in the clinical scenario of PM like mucinous carcinoma have not been studied. In this review, we divide PM into five histological types-adenocarcinomas, serous carcinomas, mucinous carcinomas, sarcomas and other rare varieties. We provide algorithms to identify the primary tumour site using immunohistochemistry when imaging, and endoscopy fails to establish the primary tumour site. The role of molecular diagnostic tests for PM or unknown origin is also discussed. Current literature on site-specific systemic therapy based on gene expression profiling does not show a clear benefit of this approach over empirical systemic therapies.

Cancer of unknown primary (CUP) encloses a group of heterogeneous tumours, the primary sites for which cannot be identified at the time of diagnosis, despite extensive investigations. CUP has always posed major challenges both in its diagnosis and management, leading to the hypothesis that it is rather a distinct entity with specific genetic and phenotypic aberrations, considering the regression or dormancy of the primary tumour; the development of early, uncommon systemic metastases; and the resistance to therapy. Patients with CUP account for 1-3% of all human malignancies and can be categorised into two prognostic subsets according to their clinicopathologic characteristics at presentation. The diagnosis of CUP mainly depends on the standard evaluation comprising a thorough medical history; complete physical examination; histopathologic morphology and algorithmic immunohistochemistry assessment; and CT scan of the chest, abdomen, and pelvis. However, physicians and patients do not fare well with these criteria and often perform additional time-consuming evaluations to identify the primary tumour site to guide treatment decisions. The development of molecularly guided diagnostic strategies has emerged to complement traditional procedures but has been disappointing thus far. In this review, we present the latest data on CUP regarding the biology, molecular profiling, classification, diagnostic workup, and treatment.

The aim of this study is to envisage a streamlined pathological workup to rule out CUPs in patients presenting with MUOs. Sixty-four MUOs were classified using standard histopathology. Clinical data, immunocytochemical markers, and results of molecular analysis were recorded. MUOs were histologically subdivided in clear-cut carcinomas (40 adenocarcinomas, 11 squamous, and 3 neuroendocrine carcinomas) and unclear-carcinoma features (5 undifferentiated and 5 sarcomatoid tumors). Cytohistology of 7/40 adenocarcinomas suggested an early metastatic cancer per se. In 33/40 adenocarcinomas, CK7/CK20 expression pattern, gender, and metastasis sites influenced tissue-specific marker selection. In 23/40 adenocarcinomas, a \"putative-immunophenotype\" of tissue of origin addressed clinical-diagnostic examinations, identifying 9 early metastatic cancers. Cell lineage markers were used to confirm squamous and neuroendocrine differentiation. Pan-cytokeratins were used to confirm the epithelial nature of poorly differentiated tumors, followed by tissue and cell lineage markers, which identified one melanoma. In total, 47/64 MUOs (73.4%) were confirmed CUP. Molecular analysis, feasible in 37/47 CUPs (78.7%), had no diagnostic impact. Twenty CUP patients, mainly with squamous carcinomas and adenocarcinomas with putative-gynecologic-immunophenotypes, presented with only lymph node metastases and had longer median time to progression and overall survival (< 0.001), compared with patients with other metastatic patterns. We propose a simplified histology-driven workup which could efficiently rule out CUPs and identify early metastatic cancer.

BACKGROUND: Head and neck squamous cell carcinomas (HNSCCs) are cancers with generally poor prognosis. Outcomes have not improved in decades, with more than half of the patients presenting with lymph node metastases at the time of diagnosis. A unique subtype of HNSCC, cancer of unknown primary of the head and neck (HNCUP) is associated with a poor outcome. Increased expression of the D2-40 gene (podoplanin) has been described for several human malignancies and has been associated with increased metastatic potential of cancer cells.
METHODS: In order to examine the role of podoplanin in lymph node metastasis of HNSCC generally and HNCUP specifically, we evaluated the prognostic impact of podoplanin expression in HNSCC- (n = 68) and HNCUP-associated lymph node metastases (n = 30). The expression of podoplanin was analyzed by immunohistochemical staining of lymph node tissue samples and correlated with clinical and histopathological data.
RESULTS: We found a non-significant tendency towards a higher podoplanin expression in HNCUP compared to HNSCC lymph node metastases and a significant correlation between a high podoplanin expression and advanced node-stage classification. Podoplanin expression had no significant impact on overall survival for both groups and did not correlate with human papillomavirus tumor status.
CONCLUSIONS: Taken together, our results suggest that upregulation of podoplanin may be associated with a stimulation of lymphatic metastasis in head and neck cancer.

BACKGROUND: Cancer of Unknown Primary (CUP) is a metastatic cancer for which the primary lesion remains unidentifiable during life and little is also known about the modifiable risk factors that contribute to its development. This study investigates whether vegetables and fruits are associated with CUP risk.
METHODS: We used data from the prospective Netherlands Cohort Study on Diet and Cancer which includes 120,852 participants aged between 55 and 69 years in 1986. All participants completed a self-administered questionnaire on cancer risk factors at baseline. Cancer follow-up was established through record linkage to the Netherlands Cancer Registry and the Dutch Pathology Registry. As a result, 867 incident CUP cases and 4005 subcohort members were available for case-cohort analyses after 20.3 years of follow-up. Multivariable adjusted hazard ratios were calculated using proportional hazards models.
RESULTS: We observed no associations between total vegetable and fruit consumption (combined or as separate groups) and CUP risk. However, there appeared to be an inverse association between the consumption of raw leafy vegetables and CUP. With respect to individual vegetable and fruit items, we found neither vegetable nor fruit items to be associated with CUP risk.
CONCLUSIONS: Overall, vegetable and fruit intake were not associated with CUP incidence within this cohort.

The World Cancer Research Fund (WCRF) and American Institute for Cancer Research (AICR) updated their cancer prevention recommendations in 2018. Adherence to these recommendations has been associated with lower cancer risk and mortality. However, adherence in relation to Cancer of Unknown Primary (CUP) risk has not been studied. This study investigates whether adherence to the WCRF/AICR recommendations is associated with CUP risk.
Data from the prospective Netherlands Cohort Study on diet and cancer was used to measure adherence to the recommendations in relation to CUP risk. The cohort includes 120 852 participants (aged 55-69 years), who completed a self-administered questionnaire on cancer risk factors at baseline. Adherence was investigated with respect to body fatness, physical activity, plant foods, meat consumption and alcohol. Incident CUP cases were identified through record linkage to the Netherlands Cancer Registry and Dutch Pathology Registry. A follow-up of 20.3 years, resulted in 856 incident CUP cases and 3911 subcohort members with complete information available for case-cohort analyses. Multivariable adjusted hazard ratios were estimated using proportional hazards models and were adjusted for age at baseline, sex, cigarette smoking (status, frequency, and duration) and total energy intake.
Highest adherence appeared to be associated with decreased CUP risk in the age-sex adjusted model (HR: 0.76, 95% CI: 0.62-0.92). After additional adjustment for cigarette smoking (status, frequency, and duration), the association attenuated and was no longer statistically significant. No multiplicative interactions were observed between sex nor smoking status and overall adherence in relation to CUP.
Within this cohort, highest adherence to the WCRF/AICR recommendations is not statistically significantly associated with decreased CUP risk after multivariable adjustment.

OBJECTIVE: Cancer of Unknown Primary (CUP) refers to the presence of metastatic lesions, with no identifiable primary site during the patient\'s lifetime. Poor survival and lack of available treatment highlight the need to identify potential CUP risk factors. We investigated whether a family history of cancer is associated with increased CUP risk.
METHODS: We performed a case cohort analysis using data from the Netherlands Cohort Study, which included a total of 963 CUP cases and 4,288 subcohort members. A Cox Proportional Hazards Regression was used to compare CUP risk in participants who reported to have a family member with cancer to those who did not, whilst adjusting for confounders.
RESULTS: In general, we observed no increased CUP risk in those who reported a family history of cancer. CUP risk appeared slightly increased in those who reported cancer in a sibling (HR: 1.16, 95% CI: 0.97-1.38), especially in those with a sister with cancer compared with those without (HR: 1.23, 95% CI: 0.99-1.53), although these findings are not statistically significant.
CONCLUSIONS: Having a family history of cancer is not an independent risk factor of CUP.

OBJECTIVE: Cancer of unknown primary (CUP) is a metastasised cancer for which no primary lesion could be identified during life. Research into CUP aetiology with respect to dietary factors is particularly scarce. This study investigates whether meat consumption is associated with CUP risk.
METHODS: Data was utilised from the prospective Netherlands cohort study that includes 1,20,852 participants aged 55-69 years. All participants completed a self-administered questionnaire on diet and other cancer risk factors at baseline. Cancer follow-up was established through record linkage to the Netherlands Cancer Registry and the Dutch Pathology Registry. A total of 899 CUP cases and 4111 subcohort members with complete and consistent dietary data were available for case-cohort analyses after 20.3 years of follow-up. Multivariable adjusted hazard ratios (HRs) were calculated using proportional hazards models.
RESULTS: We found a statistically significant positive association with beef and processed meat consumption and CUP risk in women (multivariable adjusted HR Q4 vs. Q1 1.47, 95% CI 1.04-2.07, Ptrend = 0.004 and Q4 vs. Q1 1.53, 95% CI 1.08-2.16, Ptrend = 0.001, respectively), and a non-significant positive association with processed meat consumption and CUP risk in men (multivariable adjusted HR Q4 vs. Q1 1.33, 95% CI 0.99-1.79, Ptrend = 0.15). No associations were observed between red meat (overall), poultry or fish consumption and CUP risk.
CONCLUSIONS: In this cohort, beef and processed meat consumption were positively associated with increased CUP risk in women, whereas a non-significant positive association was observed between processed meat consumption and CUP risk in men.

BACKGROUND: About five to 10% of cancers in the head and neck region are neck squamous cell carcinoma of unknown primary (NSCCUP). Their diagnosis and treatment are challenging given the risk of missing occult tumors and potential relapse. Recently, we described human papillomavirus (HPV)-related NSCCUP-patients (NSCCUP-P) as a subgroup with superior survival. However, standardized diagnostic workup, novel diagnostic procedures, decision-making in the multidisciplinary tumor board (MDTB) and multimodal therapy including surgery and post-operative radio-chemotherapy (PORCT) may also improve survival.
METHODS: For assessing the impact of standardized diagnostic processes simultaneously established with the MDTB on outcome, we split our sample of 115 NSCCUP-P into two cohorts treated with curative intent from 1988 to 2006 (cohort 1; n = 53) and 2007 to 2018 (cohort 2; n = 62). We compared diagnostic processes and utilized treatment modalities applying Chi-square tests, and outcome by Kaplan-Meier plots and Cox regression.
RESULTS: In cohort 2, the standardized processes (regular use of [18F]-FDG-PET-CT imaging followed by examination under anesthesia, EUA, bilateral tonsillectomy and neck dissection, ND, at least of the affected site) improved detection of primaries (P = 0.026) mostly located in the oropharynx (P = 0.001). From 66.0 to 87.1% increased ND frequency (P = 0.007) increased the detection of extracapsular extension of neck nodes (ECE+) forcing risk factor-adapted treatment by increased utilization of cisplatin-based PORCT that improved 5-years progression-free and overall survival from 60.4 and 45.3 to 67.7% (P = 0.411) and 66.1% (P = 0.025).
CONCLUSIONS: Standardized diagnostic workup followed by ND and risk-factor adapted therapy improves survival of NSCCUP-P.