Desmoplasia refers to the proliferation of non-neoplastic connective tissue in association with neoplasia (gives tumors a firm, fibrous, "scirrhous"
appearance) and may distort surrounding tissues. Neoplasms produce growth factors that induce formation of a stromal supporting architecture upon which they can grow.
Vascularity in neoplasms results from elaboration of growth factors that promote angiogenesis. Neoplasms must establish a blood supply to keep growing.
Necrosis in neoplasms is common because neoplastic cells function poorly and can't maintain their architecture or blood supply or metabolic demands. Necrosis becomes more likely as the size of the neoplasm increases and with decreased differentiation.
Metastases usually look similar to the primary, but not always.
The primary site is usually a single large mass in an organ, while multiple masses in an organ usually indicate metastases.
It is not always possible to tell benign from malignant based upon
histologic or cytologic criteria alone. The biologic behavior of a neoplasm may
not always correlate with the appearance, making choice of treatment more
difficult. Molecular studies may be necessary to elicit the biologic behavior of a neoplasm.