Editing Metastasis (section)

=== Metastasis and primary cancer ===
It is theorized that metastasis always coincides with a primary cancer, and, as such, is a tumor that started from a cancer cell or cells in another part of the body. However, over 10% of patients presenting to [[oncology unit]]s will have metastases without a primary tumor found. In these cases, doctors refer to the primary tumor as "unknown" or "occult," and the patient is said to have [[cancer of unknown primary origin]] (CUP) or [[unknown primary tumors]] (UPT).<ref>{{Cite journal |vauthors=Ettinger DS, Agulnik M, Cates JM, Cristea M, Denlinger CS, Eaton KD, Fidias PM, Gierada D, Gockerman JP, Handorf CR, Iyer R, Lenzi R, Phay J, Rashid A, Saltz L, Shulman LN, Smerage JB, Varadhachary GR, Zager JS, Zhen WK |date=December 2011 |title=NCCN Clinical Practice Guidelines Occult primary |journal=Journal of the National Comprehensive Cancer Network |volume=9 |issue=12 |pages=1358–1395 |doi=10.6004/jnccn.2011.0117 |pmid=22157556 |doi-access=free}}</ref> It is estimated that 3% of all cancers are of unknown primary origin.<ref name="CUP-Oncologist">{{Cite journal |vauthors=Briasoulis E, Pavlidis N |year=1997 |title=Cancer of Unknown Primary Origin |journal=The Oncologist |volume=2 |issue=3 |pages=142–152 |doi=10.1634/theoncologist.2-3-142 |pmid=10388044 |doi-access=free}}</ref> Studies have shown that, if simple questioning does not reveal the cancer's source (coughing up blood—"probably [[lung cancer|lung]]", urinating blood—"probably [[bladder cancer|bladder]]"), complex imaging will not either.<ref name="CUP-Oncologist" /> In some of these cases a primary tumor may appear later.{{citation needed|date=September 2024}}

The use of [[immunohistochemistry]] has permitted pathologists to give an identity to many of these metastases. However, imaging of the indicated area only occasionally reveals a primary.  In rare cases (e.g., of [[melanoma]]), no primary tumor is found, even on [[autopsy]]. It is therefore thought that some primary tumors can regress completely, but leave their metastases behind. In other cases, the tumor might just be too small and/or in an unusual location to be diagnosed.{{citation needed|date=September 2024}}