Classifications
Depending on how and where the CUP presents itself, and based on the histology (the study of a thin slice of tissue) and other tests, oncologists will separate CUP into categories. The metastatic (cancer-spread) distribution helps the oncologist to establish the type of cancer. Establishing this information may help give some idea of the primary location and thus help target the therapy because certain secondaries (secondary sites of the cancer) tend to come from certain primaries (primary sites of the cancer).
Certain secondaries tend to come from certain primaries
This is where the language gets complicated but it is worth at least knowing the names of some categories underlined below as they may be used by oncologists (cancer specialists) and the pattern of the cancer spread may help determine where it started. The categories below are ranked by statistical probability (that is to say Adenocarcinoma is the most common):
- Adenocarcinoma - a form of cancer that can arise in most internal organs. It is difficult for the pathologist to determine accurately the site of origin from a metastatic sample. (Carcinoma is any cancer that arises from epithelial cells - a tissue composed of a layer of cells that originates in glandular tissue. Epithelium is one of four primary body tissues.)
- Poorly differentiated cancer. A cancer that is very poorly differentiated is called anaplastic.Anaplasia is a term that refers to the histologic grade of a tumor. Anaplastic tumors are poorly differentiated, meaning that their cells do not resemble normal cells. Some very treatable cancers may be initially diagnosed as poorly differentiated. (Grade is a marker of how differentiated a cell is. Grade is rated numerically (Grade 1-4) or descriptively (e.g., 'high grade' or 'low grade'). The higher the numeric grade, the more 'poorly differentiated' or 'high grade').
- Squamous cell cancer. This is a form of cancer of the carcinoma type (a malignant tumour of epithelium) that may occur in many different organs, including the skin, mouth, esophagus, lungs, and cervix. Many of these cancers can be treated successfully.
- Neuroendocrine carcinoma. The rarest category for CUP. Neuroendocrine tumours (NETs) are tumours composed of neuroendocrine cells, which are cells that produce and secrete regulatory hormones and are present in the nervous and endocrine/hormonal systems throughout the body. Small cell carcinoma, when not in the lung, is thought to originate from neuroendocrine cells, which are found in the epithelium.
'The majority of CUP are adenocarcinomas or undifferentiated tumors; less commonly, squamous cell carcinoma, melanoma, sarcoma and neuroendocrine tumors can also present with a primary site of origin that cannot be determined.' (Source: National Cancer Institute - USA).
If no primary site is identified by the tests the oncologist uses the categories above to supplement all the information available to him or her to judge the best treatment. This may be “empiric chemotherapy”; that is to say, chemotherapy based on previous experience of patients presenting with similar characteristics.
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