Epistemic status: pretty confident but only making weak claims
In previous posts I’ve talked about how progress on cancer treatment has slowed and how recent targeted chemotherapy drugs are mostly ineffective, and floated some heuristics as to how we might approach cancer research better. In this and subsequent posts I’ll look at some examples of therapies and research directions that I think are promising. Mostly these aren’t of the form “this is a cure for cancer, go out and take it right now” so much as they are “there might be a cure for cancer around this vicinity, it needs further research, and it seems underappreciated.” I don’t claim to have an exhaustive list, but I do think I have enough examples to convince a reader that there’s a lot more interesting stuff out there than the conventional “cancer is hard because the low-hanging fruit is gone” story would imply.
In this post, I want to talk about the evidence that bacterial infections sometimes cause complete remissions in cancers.
Since the 1980s, the scientific consensus has converged on the view that the immune system destroys cancerous cells as they arise. A clinical case of cancer is simply one in which the body fails to fight off the tumor before it becomes large enough to be measurable or cause symptoms.
The current model of antitumor immunity works as follows:
Here’s how antitumor immunity is currently believed to work:
- dendritic cells sample antigens from the tumor
- dendritic cells receive a signal to mature and differentiate
- these activated dendritic cells generate T-cell responses in the lymphatic tissues
- cytotoxic T cells enter the tumor to perform their function
So activating either dendritic cells or T-cells could result in a stronger immune response to cancer. This is the theory behind many experimental immunotherapies, including cancer vaccines and CAR T-cell immunotherapy.
Spontaneous Remission and Regression
Sometimes cancer regresses or disappears by itself, without treatment; very frequently these cases follow a feverish infection. There have been many anecdotal and historical accounts of such “miraculous” recoveries, including the story of St. Peregrine.
A review  of case studies found 237 cases of spontaneous regression in 1900-1965, and 504 cases from 1966-1987. These occurred in many kinds of solid and hematological cancers. The most common kinds were kidney, neuroblastoma, malignant melanoma, choriocarcinoma, and bladder. These are not the commonest cancers; lung, colon, and breast cancer were underrepresented among spontaneous regressions. Another review  observed that “the prevalent view regarding the mechanism for spontaneous regression is the involvement of immunological factors in the host,” noting that regressing tumors have been observed to have elevated cytokine counts or elevated levels of cytotoxic lymphocytes. A 1976 survey  concluded, “Spontaneous remission of acute leukemia is associated with bacterial infection and is of short duration, weeks to months. Spontaneous regression of lymphoma or plasma cell dyscrasia is often of substantial duration, months or years, and frequently is associated with viral infections.” Another review article  confirms the relationship between bacterial infection and spontaneous remission in leukemia: “In 1950, Shear reported that brief remissions in children with untreated leukemia were observed in about 10% of the patients. Three quarters of these remissions were preceded by an episode of acute infection.”
A case study  from 1976 of a patient with malignant melanoma who refused treatment observed a spontaneous remission; there was an inflammatory reaction with lymphocytic infiltrate and increased lymphocyte cytotoxicity over the time course of regression, consistent with an immunological cause.
A case study  of acute myeloblastic leukemia found a spontaneous remission; the remission occurred after a severe febrile pneumonia, which was treated with leukocyte transfusions.
A case study  of two patients with acute myeloblastic leukemia observed that both had spontaneous remissions after infection and blood transfusions.
A case study  of a patient with acute myeloid leukemia observed a spontaneous remission after a severe streptococcal infection.
A case study  of a patient with hepatocellular carcinoma observed a spontaneous remission following massive gastrointestinal hemorrhage, shock, and blood transfusion.
A case series  of 52 patients observed that postoperative empyema (collection of pus in the body) after pneumoectomy increases five-year survival in lung cancer from 18% to 50%.
Finally, it is a traditional observation that a history of infectious disease anticorrelates with cancer risk. A literature review  found that cancer patients are less likely than healthy patients to have a history of febrile infections. “Individuals who had never experienced a febrile infectious disease were 2.5–46.2 times more likely to have developed cancer than those who had had febrile infections.”
This body of evidence suggests that the immune response to infectious disease has an antitumor effect.
In 1891, surgeon William Coley treated a patient with a sarcoma by injecting Streptococcus pyogenes culture into the tumor, and caused a complete regression and 8-year remission, after a severe erysipelas infection from which the patient almost died. Heat-killed Streptococci were safer, but didn’t have a tumor-shrinking effect. Adding heat-killed Serratia marrescens to the mixture made it effective again, and caused 60 out of 210 (29%) terminally ill sarcoma patients to have relapse-free survival of more than 10 years. By comparison, modern 5-year survival rates  for soft-tissue sarcoma are 83% for localized sarcoma, 54% for regional sarcoma, and 16% for sarcoma with distant spread. So Coley’s patients may have had better or comparable results to modern patients.
Coley tried at least 13 different vaccine formulations over time, making it difficult to compare results. “Although Coley, in his numerous publications, seldom gave full details of site, dosage, frequency, or duration of vaccine application, the optimal therapy regimen, with hindsight, seemed to be intratumoral, intramuscular, or intraperitoneal injections over long periods of time.”
Coley selected his patients deliberately to maximize the chance of recovery; he favored sarcoma patients because the bacterial vaccine seemed to work best on them. Cases of spontaneous remission following erysipelas infections were also predominantly soft-tissue sarcomas.
Coley’s preparations, known as “Coley Toxins”, were in use until 1963, when the Estes-Kefauver Act ruled that drugs had to prove safety and efficacy to be FDA-approved.
A retrospective review  published in in Alternative Therapies in Health and Medicine compared 128 Coley cases from 1890 to 1960 with 1675 controls from SEER who received a cancer diagnosis in 1983. Patients were matched by age, site, stage, and radiation treatment status. 10-year survival rate was not significantly different for Coley’s patients vs. modern controls, which suggests that Coley toxins were of comparable efficacy to chemotherapy.
A 1971 retrospective study of 47 patients with reticulum sarcoma of the bone, treated with Coley toxins before 1956, found a five-year survival rate of 64%. 22 cases (48%) achieved permanent results. With surgery or radiation therapy alone, five-year survival rates were 32-38%. As of 2015, reticulosarcoma, also known as lymphoma of the bone, has 89% five-year survival in stage I if treated with chemo + radiotherapy. But bone lymphoma is also often a sign of metastatic disease, which would have lower survival rates. 16 of the 47 cases in the 1971 study were metastatic. The failures of Coley toxins tended to be briefer courses rather than longer ones, and intramuscular rather than intratumoral or intravenous.
More recent attempts to replicate the effectiveness of Coley toxins (also known as mixed bacterial vaccine or MBV) have been less successful. A Chinese study in 1991 of 86 patients with hepatocellular carcinoma were randomized to either MBV or control; there was a nonsignificant trend towards better survival in the MBV group. An uncontrolled study  of MBV in 12 patients with refractory malignancies found one partial response, and a “dramatic improvement in performance status and disease stabilization” in a patient with AIDS and Kaposi’s sarcoma. An uncontrolled German study of 12 patients with NY-ESO-1 expressing tumors (6 melanoma, 2 sarcoma, 2 prostate cancer, 1 with head and neck cancer, 1 with bladder cancer) found one partial response after treatment with MBV.
Coley toxins are popular in alt-med circles, and the effects haven’t been replicated in a modern experiment. However, the historical data does seem to show dramatic effects, and it is mechanistically plausible that bacterial vaccines stimulate the immune system. A point in defense of Coley toxins is that the few existing modern trials don’t copy what Coley did (repeated, intratumoral injections, calibrated to produce fever, with patients selected for sarcoma). A controlled trial of Coley toxins under those conditions could be extremely valuable.
Endotoxin and Tumor Necrosis Factor
Endotoxin, also known as lipopolysaccharide, is a molecule found on the membrane of Gram-negative bacteria, which elicits a strong immune response in the host. Endotoxin causes the release of inflammatory cytokines, fever, and in extreme cases septic shock. It also has antitumor effects, strengthening the case that bacterial infection can cause cancer regression.
A study  of intravenously administered endotoxin found that it caused partial responses in 2 out of 18 patients with colorectal cancer. Intravenous endotoxin caused one complete remission out of 37 patients  with colorectal and non-small-cell lung cancer.
Parenteral injection of bacterial endotoxin in mice reliably  causes necrosis of experimental tumors. Spindle cell sarcoma (SA-1) and fibrosarcoma (Meth A) regress completely, while CaD2 (breast carcinoma) and BP3 (another kind of fibrosarcoma) grow unchanged. Necrosis occurred in all tumors. Endotoxin does not cause tumor regression in T-cell deficient mice. In mice whose tumors regressed, subsequent injection with cells from the same tumor did not grow, suggesting that sensitized T-cells are the cause of the tumor resistance.
Environmental exposure to endotoxin in Chinese workers in the textile industry is inversely associated with lung cancer risk (HR = 0.60, p = 0.002).
The anti-tumor activity of endotoxin appears to be associated with tumor necrosis factor, or TNF. In 1975  it was observed that Bacillus Calmette-Guerin-infected mice treated with endotoxin produced a substance, dubbed TNF, which was as effective as endotoxin itself in causing regression of transplanted sarcomas in mice.
TNF is too dangerous to give patients intravenously, but it is effective on sarcomas when administered locally when combined with cytotoxic chemotherapy. High-dose TNF-alpha administered in isolation perfusion of the limbs of 23 patients with metastatic melanoma or soft-tissue sarcoma found 21 complete responses and 2 partial responses. In 186 patients with locally advanced soft-tissue sarcomas, isolated limb perfusion with tumor necrosis factor caused complete response in 18%, partial response in 57%, and limb salvage in 82%.
There certainly appears to be a TNF-mediated anti-tumor response, and it is suggestive (and in line with the evidence about spontaneous remissions and Coley toxins) that this effect is associated with fever and especially strong against sarcomas.
I don’t believe there’s a single well-established bacterial cancer treatment right now, but it does seem clear that bacterial infections, particularly febrile infections, and derived substances like endotoxin and TNF, can often cause cancer remissions, especially in sarcomas and some advanced cancers. Additional “protocol engineering” followed by randomized trials might yield a reliable bacterial therapy. In the contexts where they are effective, bacterial and bacterial-derived treatments seem to cause meaningful increases in survival time, whereas most targeted chemotherapies do not.
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