|LETTER TO EDITOR
|Year : 2014 | Volume
| Issue : 2 | Page : 135-136
Carcinoma of unknown primary: An early cancer with metastasis
Manigreeva Krishnatreya, Amal Chandra Kataki, Jagannath Dev Sharma
Department of Cancer Registry and Epidemiology, Dr. B Borooah Cancer Institute, Guwahati, Assam, India
|Date of Web Publication||18-Sep-2014|
Department of Cancer Registry and Epidemiology, Dr. B Borooah Cancer Institute, Guwahati, Assam
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Krishnatreya M, Kataki AC, Sharma JD. Carcinoma of unknown primary: An early cancer with metastasis. J Med Soc 2014;28:135-6
Carcinoma of unknown primary (CUP) is defined as a metastatic tumor, when the site of the primary origin cannot be identified based on the clinical history, complete physical examination, routine laboratory tests, imaging, radio-metabolic techniques, and a careful review of the histology. In the early 1970's, it was of the view that the diagnosis of CUP could only be made if the primary tumor was not found at the autopsy.  The hypothesis of origin of CUP has been postulated in two groups by Stella et al.  The first suggests that CUP are a heterogeneous group of site-specific tumors, which share the properties of the small primary from which it derives and the second regards CUP as a distinct entity with a specific genetic asset. Currently, the use of immunohistochemistry (IHC) is often the only standard method by which a probable primary origin can be postulated.
In this retrospective analysis, the data of CUP has been obtained from the records of a hospital cancer registry of regional cancer center from January 2010 to December 2011. A total of 12,285 cancer patients were registered at our cancer registry during this period .The cases of CUP, which were considered for the analysis were based on clinical history, complete physical examination, laboratory tests, imaging techniques and histopathological or cytological examinations of specimens with immunohistochemical (IHC) staining of tissues whenever required as per the case records of the patients. In our series, of 12,285 cancer patients, 554 patients had metastasis of unknown primary. Of all CUP's, 416 (75.0%) were male and 138 (24.9%) were female patients. Mean age of patient's presenting with the CUP is 56.8 years in males and 50.6 years in females. CUP represents a heterogeneous group of malignancies that share a unique clinical behavior. The following clinical entities have been observed in our analysis; CUP of the lymph nodes in 346 (62.4%), liver in 118 (21.2%), bone in 49 (8.8%), peritoneal cavity in 15 (2.7%), lung in 11 (1.9%), pleural effusion in 8 (1.4%), brain 3 (0.5%) and ovary in 3 (0.53%) and to the skin in 1 (0.2%) patient. The common histology among the differentiated group of CUP were squamous carcinoma in 301 (57.5%), adenocarcinoma in 200 (38.3%), neuroendocrine carcinoma in 8 (1.5%), and spindle cell carcinoma in 8 (1.5%) patients. Specific tumors that presented as CUP are small cell carcinoma in 3 (0.5%) and malignant melanoma in 1 (0.2%) case out of all CUPs. In 33 (6%) patients, the differentiated histology of secondary or metastatic site was not established because of poor patient compliance. Out of metastasis to lymph nodes with unknown primary, vast majority is seen in the lymph nodes of neck 331 (59.7%) and only 13 (2.3%) of all CUPs to lymph nodes are seen in other lymphatic sites such as mediastinum, axillary, inguinal or abdominal.
Carcinoma of unknown primary accounts for 3-5% of all cancers.  In this series cancer of unknown primary accounted for 4.5% of all cancers. The occurrence of CUP in relative proportion for both males and females showed that the majority of CUP is seen at the supraclavicular lymph nodes [Figure 1]. In our registry, out of all cases of malignancies, 4054 (33%) patients were cancers of the head and neck epithelial origin. Briasoulis and Pavlidis in a certain population group have observed that CUP commonly occurs in a single site such as the liver, bone, and the lungs.  However in our series in a different population at risk the CUP mostly presented at the supraclavicular neck node accounting for 59.7% of all CUPs in the absence of origin or with a probable occult primary in the epithelial lining of head and neck region, since 90% of nodal metastasis to the neck the putative origin is from the epithelial lining in the head and neck. With the advent of newer technology the ability to predict the primary site of tumor origin in CUP is improving rapidly and the vital issue is concerning the biology, which drives early occult metastatic spread. An explanation for the enigmatic behavior of CUP can be summarized by our findings based on the known cancer site distribution in a population at risk. The pattern of occurrence of CUP is similar to that of known cancer site distribution in a population group and the same risk factors are involved for developing malignancies at different sites as well as CUP. This retrospective study can conclude that CUP is a subset of occult or small primary with early distant metastasization and not a distinct entity.
|Figure 1: The distribution of carcinoma of unknown primary in relative proportion for males and females|
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