Tetraphobia (from Greek τετράς—"tetras", "four" and φόβος—"phobos", "fear") is the practice of avoiding instances of the number . It is a superstition most common in East Asian nations.

The "British Medical Journal" reported in a study that looked at mortality statistics in the United States over a

25-year period. They found that on the fourth day of the month, Asian people were thirteen percent more likely to die of heart failure. In California, Asians were twenty-seven percent more likely to die of a heart attack on that day. The purpose of the study was to see if psychological stress caused by belief in this superstition could indeed trigger deadly heart attacks and other fatal incidents.

In 2011, coronary atherosclerosis was one of the top ten most expensive conditions seen during inpatient hospitalizations in the U.S., with aggregate inpatient hospital costs of $10.4 billion.

The relation between dietary fat and atherosclerosis is controversial. Writing in "Science", Gary Taubes detailed that political considerations played into the recommendations of government bodies. The USDA, in its food pyramid, promotes a diet of about 64% carbohydrates from total calories. The American Heart Association, the American Diabetes Association and the National Cholesterol Education Program make similar recommendations. In contrast, Prof Walter Willett (Harvard School of Public Health, PI of the second Nurses' Health Study) recommends much higher levels of fat, especially of monounsaturated and polyunsaturated fat. These differing views reach a consensus, though, against consumption of trans fats.

The role of dietary oxidized fats/lipid peroxidation (rancid fats) in humans is not clear.

Laboratory animals fed rancid fats develop atherosclerosis. Rats fed DHA-containing oils experienced marked disruptions to their antioxidant systems, and accumulated significant amounts of phospholipid hydroperoxide in their blood, livers and kidneys.

Rabbits fed atherogenic diets containing various oils were found to undergo the greatest amount of oxidative susceptibility of LDL via polyunsaturated oils. In another study, rabbits fed heated soybean oil "grossly induced atherosclerosis and marked liver damage were histologically and clinically demonstrated." However, Fred Kummerow claims that it is not dietary cholesterol, but oxysterols, or oxidized cholesterols, from fried foods and smoking, that are the culprit.

Rancid fats and oils taste very bad even in small amounts, so people avoid eating them.

It is very difficult to measure or estimate the actual human consumption of these substances. Highly unsaturated omega-3 rich oils such as fish oil are being sold in pill form so that the taste of oxidized or rancid fat is not apparent. The health food industry's dietary supplements are self regulated and outside of FDA regulations. To properly protect unsaturated fats from oxidation, it is best to keep them cool and in oxygen free environments.

The cause of neuroblastoma is not well understood. The great majority of cases are sporadic and non-familial. About 1–2% of cases run in families and have been linked to specific gene mutations. Familial neuroblastoma in some cases is caused by rare germline mutations in the anaplastic lymphoma kinase (ALK) gene. Germline mutations in the PHOX2A or KIF1B gene have been implicated in familial neuroblastoma as well. Neuroblastoma is also a feature of neurofibromatosis type 1 and the Beckwith-Wiedemann syndrome.

MYCN oncogene amplification within the tumor is a common finding in neuroblastoma. The degree of amplification shows a bimodal distribution: either 3- to 10-fold, or 100- to 300-fold. The presence of this mutation is highly correlated to advanced stages of disease.

Duplicated segments of the LMO1 gene within neuroblastoma tumor cells have been shown to increase the risk of developing an aggressive form of the cancer.

Neuroblastoma has been linked to copy-number variation within the NBPF10 gene, which results in the 1q21.1 deletion syndrome or 1q21.1 duplication syndrome.

Several risk factors have been proposed and are the subject of ongoing research. Due to characteristic early onset many studies have focused on parental factors around conception and during gestation. Factors investigated have included occupation (i.e. exposure to chemicals in specific industries), smoking, alcohol consumption, use of medicinal drugs during pregnancy and birth factors; however, results have been inconclusive.

Other studies have examined possible links with atopy and exposure to infection early in life, use of hormones and fertility drugs, and maternal use of hair dye.

Between 20% and 50% of high-risk cases do not respond adequately to induction high-dose chemotherapy and are progressive or refractory. Relapse after completion of frontline therapy is also common. Further treatment is available in phase I and phase II clinical trials that test new agents and combinations of agents against neuroblastoma, but the outcome remains very poor for relapsed high-risk disease.

Most long-term survivors alive today had low or intermediate risk disease and milder courses of treatment compared to high-risk disease. The majority of survivors have long-term effects from the treatment. Survivors of intermediate and high-risk treatment often experience hearing loss. Growth reduction, thyroid function disorders, learning difficulties, and greater risk of secondary cancers affect survivors of high-risk disease. An estimated two of three survivors of childhood cancer will ultimately develop at least one chronic and sometimes life-threatening health problem within 20 to 30 years after the cancer diagnosis.