Situations:
(1) delayed hypersensitivity skin testing site
(2) traumatic injury, including fracture (I have seen a primary squamous cell carcinoma of the lung present after a patient fractured his thumb with a hammer)
(3) recent or previous surgical site (anastomosis line, hemorrhoidectomy, old scars)
(4) other site with acute or chronic inflammation
Possible factors involved:
(1) hematogenous or lymphatic spread
(2) neovascularization at the site of injury or inflammation
(3) activation of coagulation factors, complement or other proteins
Differential diagnosis:
(1) pathologic fracture
(2) positive surgical margin
(3) direct implantation of tumor
Criteria for diagnosis:
(1) occurrence as the first manifestation of the tumor OR after a tumor free interval
(2) exclusion of other mechanisms
(3) occurrence at a site of inflammation and/or trauma
