However, new features of human cancers have been found as a result of clinical use of novel targeted therapies, angiogenesis inhibitors, and immunotherapies, including checkpoint inhibitors. if HIF-C2 there is no major clinical response. Understanding this concept is important, as concurrent and sequential therapies might lead to improved tumor responses and cures. We posit that the repertoire of tumor responses is both predictable and limited, thus giving hope that eventually HIF-C2 we can be more effective against solid tumors. Currently, among solid tumors, we observe a response of 1/3 of tumors to immunotherapy, perhaps less to angiogenesis inhibition, a varied response to targeted therapies, with relapse and resistance being the rule, and a large fraction being insensitive to all of these therapies, thus requiring the older therapies of chemotherapy, surgery, and radiation. Tumor phenotypes can be seen as a continuum between binary extremes, which will be discussed further. The biology of cancer is undoubtedly more complex than duality, but thinking of cancer as a duality may help scientists and oncologists discover optimal treatments that can be given either simultaneously or sequentially. Mutant p53 vs. loss of p16ink4a P531 and p16ink4a are the most common tumor suppressors lost in human cancer.2C6 We and others have shown that tumors with these mutations signal differently and, while this is well established in the world of basic research, it is not well appreciated by clinicians.7C9 It is well-known that certain cancer types have a large predominance of one type of tumor suppressor loss over another. For example, melanoma ranks among the top tumors for mutational burden and commonly does not express p16ink4a, but mutation of p53 is very uncommon in melanoma.10C12 On the other hand, cutaneous squamous cell carcinoma, one of the most common cancers in humans, more commonly has p53 mutation than loss of p16ink4a. 13C15 HIF-C2 Another observation is that while many tumors completely lack p16 expression, complete loss of p53 function is uncommon. This might be that having a functional p53 allele allows tumors to halt replication in response to DNA damage.16, 17 We first observed a signaling dichotomy between p53 and p16ink4a during our studies of angiosarcoma, a malignancy of endothelial cells. Rabbit polyclonal to ACSM5 In the model we generated by sequential introduction of SV40 large T antigen and oncogenic H-ras, we noted that angiogenesis and in vivo growth was regulated by phosphoinositol-3 kinase (PI3K) signaling.18 This was the first observation that PI3K regulated in vivo growth and angiogenesis of a solid tumor. 18 Since that time, activating mutations in PI3K signaling have been observed in a wide variety of human tumors. When we inhibited p42/44 MAP kinase signaling in these angiosarcoma cells, we noted slowed growth, but more aggressive in vivo growth and production of matrix metalloproteinases.7 Thus, in this system, MAP kinase HIF-C2 was acting as a tumor suppressor, in contradiction to its well-known oncogenic activity in NIH3T3 fibroblasts. In order to understand the context difference in signaling, we noted that NIH3T3 fibroblasts have lost p16ink4a expression,19 while our angiosarcoma cells have defective p53 signaling.18 We thus hypothesized that p42/44 MAP kinase signaling is oncogenic in the context of loss of p16ink4a, but may be tumor suppressive in the mutant p53 context. In fact, this has been elegantly demonstrated accidentally in patients receiving the Braf inhibitor vemurafenib, which inhibits p42/44 MAPK signaling in melanoma, but can provoke squamous cell carcinoma, which has p53 mutations.14 The major discovered differences between these tumors have increased and are summarized in Table?1. Table 1 Signaling differences and mutations in tumors that have either mutant p53 or loss of p16ink4a thead th rowspan=”1″ colspan=”1″ Mutant p53 /th th rowspan=”1″ colspan=”1″ Loss of pl6 /th /thead p42/44 MAPK possible tumor suppressorp42/44 MAPK pro-tumorigenicNegative for Wilms Tumor 1Positive for Wilms Tumor 1Ameboid morphologyMesenchymal morphologyLymph nodesHematogeneusRadiation sensitiveRadiation resistantNotch inactivateNotch activationSurvivin Superoxide Stat 3Stat 3/5Hif1Hif2Extracellular membrane depositionIncreased telomerase Open in a separate HIF-C2 window These represent polar opposites, but in some very advanced tumors, there may be both mutant p53 and loss of p16ink4a, leading to potential signaling plasticity Patterns of carcinogenesis It is well-known that.