My first significant thought (which came up a bit in the AIs’ output) is that it would seem that, if fungi cause cancer, then the fungi would at least sometimes be transmitted from one person to another, and if you weren’t aware of the fungi, then this would look like cancer being transmitted from one to the other. Yet I think this has basically never been observed.[1]
One could try supposing that each fungus is only rarely able to infect people—only the few individuals that are unusually vulnerable to it. But, well. I imagine that would generally include anyone whose immune system is crippled. Surely there have been enough cases of people with cancer next to old, immunocompromised people in a hospital, with sufficient mistakes in hygiene that the one would have infected the other. Maybe there are additional requirements for an individual to be infected (the fungus has a favorite temperature? Acidity? Salt level?)… but even taking that into account, I think there should have been enough cases that we would have noticed. (If the chance of an individual being infectable by a given fungus is so low that we never see transmission, then how is it that, er, 1/6th of all deaths are caused by cancer? There would have to be zillions of different fungi, each of which is able to infect only a tiny number of people… which surely would have led to natural selection for much better infectivity by now?)
Incidentally, I think it is known that there are some viruses (like HPV) that cause (or greatly heighten the risk of) cancer. It’s plausible that fungi play a significantly larger role of this type than people realize. But for it to be the primary cause seems implausible.
The strongest evidence is that they found cancers that seem to have no mutations.
It probably takes years before a tumor grows big enough for normal methods to detect it.
There exist fast-growing cancers. I figure that if the fungi theory is correct, then probably a good amount of this is caused by the specific fungus (and perhaps what part of the body that fungus targets), and most of the rest comes from the target’s immune system (not sure what else would contribute significantly). If transmission and mild infections are common, and if, say, 1% of cancers are fast-growing, I feel like there should be lots of cases where an immunocompromised person picks up a fast-growing cancer fungus at a hospital or something and, within a few years, gets diagnosable cancer. Enough that it should have been noticed. I don’t have numbers for this, but that’s my suspicion.
Or, for example… How often do couples get the same type of cancer? I found this:
METHODS
The authors identified 25,670 cancer-free married couples in northern California who were followed for up to 31 years for the development of cancer. In Cox proportional hazards analysis, the development of cancer in a spouse was treated as a time-dependent, independent variable, and spouse-with/spouse-without risk ratios were determined, controlling for age and gender. For selected concordant espoused pairs, additional explanatory information was sought in their medical records.
RESULTS
There was no excess concordance for all cancers combined; the spouse-with/spouse-without risk ratio was 0.97 (95% confidence interval, 0.90–1.05). Statistically significant husband-wife associations were found only for cancer of the tongue and stomach and for non-Hodgkin lymphoma. Except for cancer of the penis/endometrium and testis/vulva, based on one couple with each combination, gender specific cancers did not aggregate within married couples. Established and suspected risk factors, not necessarily related to the marriage, were found for some individuals who had concordance with their spouses.
CONCLUSIONS
Little spousal concordance for cancer occurrence was found. The study of spousal aggregation does not appear useful in identifying unsuspected environmental causes of cancer in heterogeneous populations in urban areas of affluent Western countries. A cohort study would have to be much larger than this one to detect weak spousal concordance reliably..
Also, for whatever Claude’s opinion is worth:
Q: How often do couples get the same type of cancer?
While it’s not extremely common for couples to get the same type of cancer, it does happen occasionally. This phenomenon has been studied, and there are several factors to consider:
Shared environmental factors: Couples often share the same living environment, diet, and lifestyle habits, which can expose them to similar cancer risk factors.
Similar behaviors: Shared behaviors like smoking, alcohol consumption, or sun exposure can increase risk for certain cancers in both partners.
Infectious agents: Some cancers are caused by infectious agents (like HPV for cervical cancer), which can be transmitted between partners.
Age-related risks: As couples age together, they may face similar age-related cancer risks.
Genetic factors: While not directly shared between couples, people might choose partners with similar genetic backgrounds, potentially influencing cancer risk.
Coincidence: Given the prevalence of cancer, some couples will develop the same cancer by chance.
Screening effect: When one partner is diagnosed, the other may be more likely to get screened, potentially leading to a diagnosis of a cancer that might have otherwise gone undetected.
Studies on this topic have shown:
A slight increase in cancer risk for partners of cancer patients, but this varies by cancer type.
Higher correlations for smoking-related cancers, suggesting shared lifestyle factors play a role.
Increased risk for cancers with infectious causes, like stomach cancer (H. pylori) or liver cancer (hepatitis viruses).
It’s important to note that while interesting, these occurrences are not common enough to be considered a significant public health concern.
Genes vs environment seems like an obvious thing to track. Most people in most places don’t move around that much (unlike many members of our community) so if cancers are contagious for many cancers, especially rarer ones, you’d expect to see strong regional correlations (likely stronger than genetic correlations).
Maybe? It doesn’t seem very common for infectious diseases to remain in one area. It depends a lot on how they are transmitted.
It’s also not unusual for a non-infectious disease to have significant geographical patterns.
There are cancers which are concentrated in particular areas, but there seem to be guesses for those patterns that don’t depend on fungal infections.
My first significant thought (which came up a bit in the AIs’ output) is that it would seem that, if fungi cause cancer, then the fungi would at least sometimes be transmitted from one person to another, and if you weren’t aware of the fungi, then this would look like cancer being transmitted from one to the other. Yet I think this has basically never been observed.[1]
One could try supposing that each fungus is only rarely able to infect people—only the few individuals that are unusually vulnerable to it. But, well. I imagine that would generally include anyone whose immune system is crippled. Surely there have been enough cases of people with cancer next to old, immunocompromised people in a hospital, with sufficient mistakes in hygiene that the one would have infected the other. Maybe there are additional requirements for an individual to be infected (the fungus has a favorite temperature? Acidity? Salt level?)… but even taking that into account, I think there should have been enough cases that we would have noticed. (If the chance of an individual being infectable by a given fungus is so low that we never see transmission, then how is it that, er, 1/6th of all deaths are caused by cancer? There would have to be zillions of different fungi, each of which is able to infect only a tiny number of people… which surely would have led to natural selection for much better infectivity by now?)
Incidentally, I think it is known that there are some viruses (like HPV) that cause (or greatly heighten the risk of) cancer. It’s plausible that fungi play a significantly larger role of this type than people realize. But for it to be the primary cause seems implausible.
This seems worth digging into.
There are a few cases of cancers where it’s known that the actual cancer cells themselves go from organism to organism: https://en.wikipedia.org/wiki/Clonally_transmissible_cancer
How would transmission be detected? It probably takes years before a tumor grows big enough for normal methods to detect it.
I assume that transmission is common, mild infections are common, and they rarely become harmful tumors.
There exist fast-growing cancers. I figure that if the fungi theory is correct, then probably a good amount of this is caused by the specific fungus (and perhaps what part of the body that fungus targets), and most of the rest comes from the target’s immune system (not sure what else would contribute significantly). If transmission and mild infections are common, and if, say, 1% of cancers are fast-growing, I feel like there should be lots of cases where an immunocompromised person picks up a fast-growing cancer fungus at a hospital or something and, within a few years, gets diagnosable cancer. Enough that it should have been noticed. I don’t have numbers for this, but that’s my suspicion.
Or, for example… How often do couples get the same type of cancer? I found this:
Also, for whatever Claude’s opinion is worth:
My guess is that almost nobody looks for this kind of connection.
Even if they do notice it, they likely conclude that pathogens are just another small influence on cancer risk.
Genes vs environment seems like an obvious thing to track. Most people in most places don’t move around that much (unlike many members of our community) so if cancers are contagious for many cancers, especially rarer ones, you’d expect to see strong regional correlations (likely stronger than genetic correlations).
Maybe? It doesn’t seem very common for infectious diseases to remain in one area. It depends a lot on how they are transmitted. It’s also not unusual for a non-infectious disease to have significant geographical patterns. There are cancers which are concentrated in particular areas, but there seem to be guesses for those patterns that don’t depend on fungal infections.