Tyrosine isomers mediate the classical phenomenon of concomitant tumor resistance.

Concomitant tumor resistance (CR) is a phenomenon originally described in 1906 in which a tumor-bearing host is resistant to the growth of secondary tumor implants and metastasis. Although recent studies have indicated that T-cell-dependent processes mediate CR in hosts bearing immunogenic small tumors, manifestations of CR induced by immunogenic and nonimmunogenic large tumors have been associated with an elusive serum factor. In this study, we identify this serum factor as tyrosine in its meta and ortho isoforms.

Tumor transition zone: a putative new morphological and functional hallmark of tumor aggressiveness.

A small primary or secondary tumor load can occasionally induce more deleterious effects than a histologically identical larger one. In the four murine models studied herein this enhanced tumor aggressiveness could not be attributed to NRAS mutations or other hereditary changes, differential vascularization of live tumor tissues, or necrosis content. Instead, the main tumor feature associated with a more aggressive behavior was the presence of a high number of vessels, sometimes filled with inflammatory cells, inside a tumor area, which we have identified and designated as the transition zone between the live and the necrotic zones.

Embryonal mass and hormone-associated effects of pregnancy inducing a differential growth of four murine tumors.

A differential effect of pregnancy on the growth of subcutaneous implants of four murine tumors has been observed. Two tumors lacking receptors for progesterone and estrogen [methylcholanthrene-induced fibrosarcoma (MC-C) and spontaneous lymphoid leukemia (LB)] exhibited slow kinetics throughout the course of pregnancy, although inhibition was stronger beyond day 10. On the other hand, one of two tumors bearing receptors for progesterone and estrogen [medroxyprogesterone (MPA)-induced mammary adenocarcinoma (C7HI)] exhibited three phases: up to days 8-10 of gestation the tumor grew faster than in virgins, between days 8-10 and 15 it reached a plateau, and beyond day 15 a sharp reduction in tumor mass was observed.