The pathology of tumor stromatogenesis.

Stromatogenesis is the formation of new, specific type, stroma at sites of active tumor cell invasion as an integral part of the invading process. The newly formed stroma by being wedged between tissue planes of least resistance disrupts the continuity of normal structures cleaving paths for the invading tumor cells--intramural stromatogenesis for endophytic tumors. Less frequently, the new stroma is formed towards a void space, i.e. at the free surfaces, whether internal or external (extramural stromatogenesis for exophytic tumors). It is postulated that the formation of this new stroma is generated and governed by the invading tumor cells with the tolerance and complicity of the adjacent activated fibroblasts. The spindle cells of the "neostroma" are intensely proliferating myofibroblasts, which are characterized by the frequent expression of α-smooth muscle actin and the particularly frequent expression of thymidine phosphorylase, PDGF-receptors and SPARC (secreted protein acidic rich in cysteine). The cellular and extracellular qualities, different as they are from those of reactive fibrosis, make stromatogenesis amenable to easy penetration by neoplastic cells and a prospective method for diagnosing early tumor invasion. Studies also suggest that the neostroma has complementary to cancer cell metabolic activity, important for buffering of cancer cell waste products and for the prevention of cancer cell acidic death. Thus, cancer cells and neostroma should not be seen as a mixture of heterogeneous uncoordinated cells but rather as a unified morphologic and metabolic domain with a harmonious collaboration between aerobic (myofibroblasts, endothelial cells) and anaerobic compartments (cancer cells).