Do Some Breast Cancers Go Away on Their Own?

breast-cancer-research-ZahlIs it possible that as much as 35% of   invasive breast cancers will go away on their own if left alone? This is the conclusion of Norwegian researcher Dr. Per-Henrik Zahl, who analyzed data from more than 600,000 Swedish women, half of whom had regular mammogram screening and half who did not. Dr. Zahl suggests that breast cancers may be over diagnosed, in much the same way that prostate cancers are over diagnosed. The study was published in Lancet Oncology.

What makes this study especially useful is that the so-called “in situ” cancers such as ductal carcinoma in situ (DCIS) were excluded. In most cases, DCIS would be better defined as a pre-cancer, just as stage 1 and 2 pap smears are considered pre-cancers. It makes sense that many, if not most “in situ” cancers would go away on their own. This evidence that invasive cancers may also go away on their own is very important, because it could save tens of thousands of women from unnecessary surgery.

Dr. Zahl recommends treating women with small tumors, identified by needle biopsy as estrogen-receptor positive, with tamoxifen or an aromatase inhibitor.  Both reduce the incidence of breast cancer but have serious side effects. Breast cancer risk can be reduced in many ways, including hormone balancing, good vitamin D levels, avoiding toxins such as pesticides, a wholesome diet and stress management. If women were counseled on these risks, and given support for making the necessary lifestyle changes, odds are good these tiny cancers would regress. I recommend the book What Your Doctor May Not Tell You about Breast Cancer (Lee, Zava, Hopkins) for a better understanding of what causes breast cancer and what can be done to prevent it.

The Zahl study was very complex so I got in touch with Dr. David Zava, co-author with Dr. John Lee and myself of What Your Doctor May Not Tell You about Breast Cancer, and asked him to comment on this important research. Here’s what he had to say:

“What Zahl is suggesting is that based on the difference in controls (non screened) and screened women, about 35% of invasive tumors grow to just below detection level (about 1 cm) and then spontaneously regress.  Why this regression happens in some tumors and not others is unknown, but is probably related to a shift in the woman’s hormonal milieu. In perimenopausal women, we know that estrogens are often excessive and progesterone can be very low. So, tumors stimulated by estrogen during this hyper-estrogenic phase would spontaneously regress as estrogen begins to drop with menopause. Alternatively, progesterone could  help correct this imbalance, causing tumor regression to occur in even more than 35% of the cases. The work of Micheli (2004) showing that the higher the endogenous [made in the body] progesterone the lower the incidence of breast cancer, is supportive of this concept.

“I believe that small invasive breast cancers that are beginning to form in the body are more likely to melt away if the hormonal environment that causes them to form in the first place corrects itself either on its own, or with hormones that counter the growth-promoting actions of estrogens, such as progesterone, testosterone, aromatase inhibitors, or anti-estrogens like tamoxifen. When you think of physicians like our mentor John Lee, Helene Leonetti, and others, who find little breast cancer in their clinical practice, the reason, I believe, is because they identify and correct hormonal imbalances, which would cause small lesions to regress.

“I found it interesting that Zahl did conclude more should be done to study the relationship of the hormonal milieu to the incidence of tumor growth and spontaneous tumor regression. Having worked in the field of breast cancer and hormone testing for the past 35 years I concur with Zahl that we need to identify women with hormonal risk profiles for breast cancer and correct these imbalances with lifestyle changes (improved diet, exercise, nutritional supplements) and hormone therapy if needed. Such a wholistic approach  was the basis of John Lee’s clinical practice, and he had very few patients with breast cancer.”

It will probably take a decade or more for various scientists and doctors to take this evidence into account and change the way breast cancer is treated. But women can educate themselves now about risk factors for breast cancer, and think twice before getting surgery for a tiny cancer. Watchful waiting will likely end up being a wise choice for many breast cancers, just as it is for prostate cancer.


Zahl PH, Gotzsche PC, Maehlen J, “Natural history of breast cancers detected in the Swedish mammography screening programme: a cohort study,” Lancet Oncol. 2011 Nov ;12(12):1118-24.

Micheli A, Muti P, Secreto G, “Endogenous sex hormones and subsequent breast cancer in premenopausal women,” Int J Cancer. 2004 Nov 1;112(2):312-8.

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