Re: How can you tell if a tumor is cancerous or benign -if it will metastasize?

Dear Brent:
Yes, there are many differences between primary (not metastatic)
malignant tumors (cancers) and benign tumors, both to the unaided eye
(gross pathology) and the microscope-aided eye (histopathology).  Let's
assume for simplicity that all cancers, irrespective of their origin in
a specific organ or tissue, have the same appearance.  This table lists
some of the diagnostic criteria used by pathologists to arrive at this
distinction:

		PRIMARY MALIGNANT		BENIGN

CLINICAL	rapid growth			slow growth
HISTORY		family history of cancer	no family history

GROSS		bleeding			no bleeding
PATHOL		tumor margins indistinct	tumor margins distinct
		satellite tumors		no satellite tumors

		
MICRO		cells infiltrate surrounding	cells push surrounding tissues
PATHOL			tissues				aside
		cell clumps detach from		cells remain attached to main
			main tumor			tumor
		cells die (necrosis) easily	no cell necrosis
		cells invade blood vessels	no blood vessel invasion
		cells are enlarged with		cells normal in size/shape
			bizarre shapes
		tumor nuclei large, irregular,	tumor nuclei uniform size,
			and stain "dark blue"		stain "pale blue"
		mitotic figures common and	mitotic figures absent or at
			abnormal in shape		most very rare

This serves as a generalized answer to your question as it pertains to
PRIMARY CANCER.  This decision is of vital importance, since it will
determine the patient's clinical treatment and expected outcome. 
Remember, however, that cancers are really not all the same.  There are
numerous OTHER pathological and clinical CRITERIA that help make this
separation, particularly criteria that are primary tumor specific, i.e.,
thyroid gland, breast, prostate gland, etc.  (Metastatic or secondary
tumors may be discovered in almost any location and are not the subject
of this response.)  Thank you for your thoughtful question and good luck
in your life-long learning adventure.

Sincerely,
Scott