Among those children who received an intramuscular injection of vitamin K, the risk of cancer was 2 times higher. A similar result was obtained in another study by the same authors.
This essentially means that prevention of 30-60 cases of hemorrhagic disease will lead to 980 additional cases of cancer.
The fact that human evolution allowed the development of vitamin K deficiency in normal breastfed babies, which leads to a small risk of hemorrhagic disease, have always been perceived as physiologically flawed. The most likely explanation for this phenomenon is that there is some evolutionary advantage that outweighs this risk.
It is possible that relative vitamin K deficiency in the critical phase of rapid growth may protect vulnerable tissues from mutagenesis.
The probability of bleeding among infants not belonging to any risk group is 1 in 10,000. Among those who received the injection, the probability of bleeding is 1 in a million.
In this study, cancer (mainly leukemia) was associated with an intramuscular injection of vitamin K (OR = 1.44, CI: 1.00–2.08). Children who were diagnosed before the age of 12 months were excluded from the study.
Several more studies had been conducted that did not find a correlation between injection and increased risk of cancer. In this study, there was no correlation between injection and cancer in general, although a correlation with acute lymphoblastic leukemia before the age of 6 was found (OR=1.79).
At the moment, it is believed that there is no connection between vitamin K injections and increased cancer incidence rate. However, randomized trials have not been conducted, and a small increase in risk cannot be ruled out.
The authors believe that injections should only be administered to infants at risk.
The authors analyzed 6 studies on association between vitamin K injections and cancer, and concluded that if the data to be analyzed in a certain way, no association between the risk of leukemia and the injection can be found, but use of revised analysis methods demonstrates a moderate association (OR = 1.21, CI: 1.02-1.44). When just a single study was excluded from the analysis, the statistical significance disappeared (OR = 1.16, CI: 0.97-1.39).
The authors conclude that although it is impossible to fully negate moderate association, there is no convincing evidence that vitamin K injection is associated with leukemia.
In patients with cancer of mice, which reduced the level of vitamin K in the diet, there was significantly less metastasis than in mice in the control group.The metastasis was influenced by the level of vitamin K, rather than blood coagulation, since anticoagulants were not affected on the number of metastases.Observations on vitamin K deficiency in the fetus and newborn: has made by mistake? 1995, Israels, Semin Thromb Hemost
The fetus of mammals and bird embryos has a significantly lower level of vitamin K than adults, and it's unclear why a normal newborn enters the outside world in a state that requires immediate intervention. The question why even adults do not have excess vitamin K , also remains unanswered.
Benzopyrene is a carcinogen for mice. In mice on a diet with a low level of vitamin K, tumors after the administration of this drug developed much more slowly than in mice on a normal diet.
In mice injected with vitamin K in addition to benzapyrene, the tumors developed faster.
When mice were given only vitamin K, without benzapyrine, the tumors did not develop.
The authors suggest that a low level of vitamin K the fetus is a secondary defense mechanism against xenobiotics that pass through the placenta.
BCG vaccination is associated with a 27% reduction in the risk of leukemia.BCG vaccination and the subsequent development of cancer in humans. 1981, Kendrick, J Natl Cancer Inst
Although when considering all types of cancer, BCG vaccination has been associated with an increased risk of cancer by 13%. More:   
After BCG vaccination was discontinued on the southern island of New Zealand, and uphold on the northern island, the death rate from non-Hodgkin's lymphoma increased on the northern island and decreased on the southern island, although it was the same before. The authors conclude that the proposals for using BCG against leukemia are unreasonable.
Varicella in childhood is associated with a decrease in the risk of cancer by 34%. Having three common colds per year decreases the risk of cancer by 77%-82%. Viral gastroenteritis – by 57%. High frequency of infections decreases the risk of cancer by 53%. Measles, mumps and rubella also decrease the risk of cancer by 17%-39%, but the result was not statistically significant.
Two hundred cancer patients got intravenous injections of mumps virus (Urabe strain). The only side effect was a slight fever in half of the patients.
In 26 patients regression of the tumor was observed. In majority of the patients the pain was alleviated. In 30 out of 35 patients, the bleeding decreased or stopped. In 30 out of 41 patients, ascites and swelling decreased or disappeared.
All three of the previous studies were conducted in Japan, and the results were of no interest to anyone outside the country. Then, in 2016, the notorious Mayo Clinic decided to take samples of this virus from Japan and test them in vitro and on mice. It turned out that indeed, the virus has an anti-cancer effect.Febrile infectious childhood diseases in the history of cancer patients and matched controls. 1998, Albonico, Med Hypotheses
Rubella in childhood is associated with a 62% reduction in the risk of various cancers (not including breast cancer) and chickenpox by 38%. Measles and mumps are associated with a 10-15% reduction in cancer risk (but not statistically significant)
One or more children's febrile illnesses are associated with a 73% reduction in the risk of cancer.
Those who did not have measles in their childhood (or had a sick atypical, without a rash, like after vaccination) had an increased risk in adulthood: 1) immunoreactive diseases (autoimmune diseases due to an infectious disease),
2) skin diseases (dermatitis, eczema, etc.),
3) degenerative bone and cartilage disease (osteoarthritis, etc.),
4) oncological diseases.