Tumor fever:

http://www.cancersourcern.com/Nursing/CE/CECourse.cfm?courseid=133&contentid=22349

Tumor Fever

Fever of unknown origin (FUO) in patients with cancer is a diagnosis of
exclusion. If the patient is not neutropenic, and there is no source of
infection or fever found despite rigorous evaluation, then the fever is
likely due to the tumor. Cytokines are known to be involved in the acute
phase response, and IL-1 (endogenous pyrogen) is well known to cause
fevers. In addition, other cytokines are most likely involved, such as
Tumor Necrosis Factor (TNF alpha and beta), interferon, and IL-6. TNF
appears to work differently from IL-1, and in fact, may induce its
pyrogenic activity (Arnold et al, 2001). Cancers most likely to cause
tumor fever are lymphoma, solid tumors, which have metastasized to the
liver or CNS, and hypernephroma (Cunha, 1996). Fevers associated with
lymphomas ("B" symptom) confer a worse prognosis. Patients with Hodgkin's
Disease may have intermittent fever that is predictible in timing. [other
causes are mentioned there]

http://www.google.com/groups?hl=en&lr=&ie=UTF-8&c2coff=1&selm=326d9774.11700565%
40nntp.ix.netcom.com

Sometimes with advanced cancers, there can be fever.  It is presumed to be
perhaps due to necrosis (or death) of central areas of the tumor, or the
body's immune response to the tumor, or the response to products released
from the tumor.  It is a diagnosis often made by exculusion, since you
have to rule out bacterial, viral and fungal infections first.
Sometimes these fevers will respond to non-steroidal antiinflammatory
drugs, like naproxen, but the response is not specific to tumor fever as
fever from many causes can also respond.  Of course, patients with
metastatic cancer are at higher risk of a variety of infections, and we
usually end up putting them on antibiotics first, and consider tumor fever
only after a search has failed to reveal infection, and there's been no
response to
antibiotics. H2

http://www.google.com/groups?selm=W1_Wb.54024%24Wa.44337%40news-server.bigpond.n
et.au&output=gplain

When a tumour 'outgrows itself' it can die and starts to break down, this
also happens with successful chemo and radiotherapy. When tissues break
down toxins are released (as when the body's white cells fight infection)
These
toxins can cause many of the symptoms associated with infection including
nausea, fever, rigors, sweating etc.

An oncologist I worked with used to give naprosyn or indocid and if this
resolved the symptoms then he could fairly safely assume the problem was
related to tumour breakdown and not infection....something to do with
chemicals blocked by the naprosyn that would not be present in infection.