How would you differentiate between an enlarged testis
caused by orchitis and cancer of the testis?

Orchitis is acute inflammation of the testes. Orchitis
is uncommon and usually caused by epididymitis or
systemic infection (common with the mumps). The onset of
orchitis is quick, usually within 3-4 days. The
individual with orchitis usually has a high fever (up to
40 degrees Celcius) “marked prostrations, bilateral or
unilateral erythema, edema, and tenderness of the
scrotum, and leukocytosis (Mc Cance & Huether, 2006, p.
810)”. 

In contrast, cancer of the testis is usually gradual and
painless, although there may be a “testicular heaviness
or dull ache in the lower abdomen (Mc Cance & Huether,
2006, p. 811)”. However, there is occasionally acute
pain associated with rapid growth causing hemorrhage and
necrosis (Mc Cance & Huether). Upon palpation, abnormal
consistency, irregularity of the testis, nodularity,
diffuse enlargement, or nontender masses are usually
found (Mc Cance & Huether). Blood work will show
increased tumor markers, at times before the tumor is
large enough to palpate. Although cancer of the testis
is one of the most curable cancers, it is often not
detected until there symptoms of metastases (10% of
individuals) (Mc Cance & Huether). 

So, if a male is complaining of a new pain, it is more
likely that he has orchitis than testicular cancer. This
reinforces the importance of monthly self exams for
males as tumors can be asymptomatic until they have
progressed to more dangerous stages.

References

McCance, K. L., & Huether, S. E. (2006).
Pathophysiology: the biologic basis for disease in
adults and children. Elsevier Mosby: Philadelphia.