Soybean Protein Inhibits Colon, Liver, Lung Cancers

At least it does in the lab:

Peptides Derived From High Oleic Acid Soybean Meals Inhibit Colon, Liver And Lung Cancer Cell Growth, Food Research International, 2012

"Soybean meal, a co-product after oil extraction from seeds, is rich in protein. Our objective was to utilize this co-product, obtain gastrointestinal (GI) resistant peptides from the isolated protein, and test for bioactivity against colon, liver and lung cancer cell lines.

Peptide fractions showed cell growth inhibition of 73% of colon cancer, 70% of liver cancer cells and 68% of lung cancer cells. Dose response showed that the peptides had significant inhibitory effect at higher concentrations and gradually decreased with decreased dosage.

Soybean peptide fractions can thus be a source of bioactivity against colon, liver and lung cancer cell proliferation."

Peptides, or small bits of protein derived from defatted soybean meal significantly inhibited colon cancer cell growth by 73%, liver cancer cell growth by 70%, and lung cancer cell growth by 68%. The higher the dose, the more the cancer-inhibiting effect.
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That was in vitro. Here's a study in women:

Prediagnosis Soy Food Consumption And Lung Cancer Survival In Women, Journal of Clinical Oncology, March 2013

"This analysis included 444 women with incident lung cancer identified from the Shanghai Women's Health Study.

Higher intake of soy food was associated with better overall survival after adjusting for demographic and lifestyle characteristics and other nonclinical factors. Larger effect sizes for the association were found after additional adjustment for tumor stage and treatment.

This study suggests, to the best of our knowledge for the first time, that, among women with lung cancer, prediagnosis intake of soy food is associated with better overall survival."

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And by the same authors a few months earlier:

Soy Food Intake and Risk of Lung Cancer: Evidence From the Shanghai Women's Health Study and a Meta-Analysis, American Journal of Epidemiology, October 2012

"Included in the analysis were 71,550 women recruited into the Shanghai Women's Health Study.

During a mean follow-up period of 9.1 years, 370 incident lung cancer cases were identified; 340 patients were lifetime never smokers.

After adjustment for potential confounders, soy food intake was inversely associated with subsequent risk of lung cancer (P trend = 0.004); the hazard ratio for the highest quintile of intake compared with the lowest was 0.63 (95% confidence interval: 0.44, 0.90).

Meta-analysis of 7 studies conducted among nonsmokers found a summary relative risk of 0.59 (95% confidence interval: 0.49, 0.71) for the highest categories of soy or isoflavone intake versus the lowest.

This study suggests that soy food consumption may reduce lung cancer risk in nonsmoking women, particularly for aggressive tumors, and its effect may be modified by endogenous estrogens."

The risk reduction was similar in both the Shanghai study and the meta-analysis. Women who ate the most soy food cut their risk of lung cancer by about a half, compared with women who ate the least soy.

In these studies, eating soy food cut both the risk of getting cancer, and the progression of cancer.
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