The chapter on cancer of the penis in a new edition of an authoritative Oxford textbook on cancers points out that cancer of the penis is an extremely rare disease (in fact, less common than cancer of the male breast) and that the risk factors are preventable conditions, including pathological phimosis and infection with human papilloma virus. The foreskin is not a risk factor for cancer of the penis, and circumcision does not infallibly prevent it. The summary of the chapter follows:
Penile cancers are rare primary malignancies located on the glans, foreskin, or shaft of the penis,
excluding the urethra. The vast majority of penile cancers are epithelial tumors representing
histological subtypes of squamous cell carcinoma (SCC). Most penile SCCs are believed to develop
through preinvasive lesions known as penile intraepithelial neoplasia and penile carcinoma in situ.
Penile cancers account for 0.1%–0.3% of all incident cancers (excluding non-melanoma
skin cancers) in the United States and other developed countries and up to 1% of all cancers in some
countries in sub-Saharan Africa. Annual incidence rates per 100,000 men (world standardized) are
typically between 0.3 and 1.0 in developed countries, being 0.5 in the United States. During 2002–
2011, SEER data showed rather stable penile cancer rates with no statistically significant changes in
incidence or mortality.
Being rare in men younger than 40 years, penile cancers are typically diagnosed among men
above age 60. The 5-year relative survival rate after penile cancer was 67% for all stages combined
in US patients recorded in SEER registries during 2004–2010, with foreskin cancers having a more
favorable prognosis than cancers at other penile sites.
The two most important risk factors for penile cancer are pathological phimosis and
infection with high-risk types of human papillomaviruses (HPV), which are both preventable
conditions. Non-surgical strategies to reduce the frequency of pathological phimosis need
consideration, particularly because rates of newborn circumcision are declining in the United States
and elsewhere. Increased awareness among doctors and parents about the importance of non-interference
with the physiological foreskin separation process in young boys, and the promotion of
safe-sex practices, possibly combined with preadolescent gender-neutral HPV vaccination
programs, will likely reduce the frequencies of pathological phimosis and sexually acquired HPV
infections and, eventually, reduce the burden of penile cancer at the population level.
Source: Frisch M. 2018. Penile Cancer. In: Thun M J, Linet M S, Cerhan J S, Schottenfeld D (Eds.), Cancer Epidemiology and Prevention (4th ed., pp. 1029-1038). Oxford University Press, New York.
Smegma is not carcinogenic
Despite the importance of avoiding smegma so frequently stressed by enthusiasts for routine circumcision, there is no evidence at all that smegma is harmful. Why would it be? It's just a natural secretion like saliva, found in the genitals of both males and females.
The carcinogenicity of smegma: Debunking a myth
RS Van Howe,* FM Hodges‡
*Department of Pediatrics, Michigan State University School of Human Medicine, Marquette, MI and ‡Berkeley, CA, USA, in Journal of the European Academy of Dermatology and Venereology, Vol. 20, 2006, pp. 1046-1054
Abstract
Background: Smegma is widely believed to cause penile, cervical and prostate cancer. This nearly ubiquitous myth continues to permeate the medical literature despite a lack of valid supportive evidence.
Methods: A historical perspective of medical ideas pertaining to smegma is provided, and the original studies in both animals and humans are reanalysed using the appropriate statistical methods.
Results: Evidence supporting the role of smegma as a carcinogen is found wanting.
Conclusions: Assertions that smegma is carcinogenic cannot be justified on scientific grounds.
Extract from the conclusion
The evidence does not support the theory that smegma is a cause of genital cancer. The smegma theory of disease was best stated by Boczko and Freed: "Smegma, a sterol, produced by Tyson’s glands in the epithelium of the retroglandular sulcus, has been implicated as the causative agent. It may be converted to a carcinogen by the action of the Mycobacterium smegmatis." [69] From the medical literature we have found that smegma is not a sterol, that there are no Tyson’s glands, that smegma is not converted to a carcinogen by M. smegmatis, and that M. smegmatis is not part of the normal genital flora. The myth is sustained only by its popularity among circumcision advocates.
Some have extrapolated the smegma theory by hypothesizing that men with inadequate circumcisions may be at risk for cancer because smegma can accumulate under any foreskin remnants. [70] In similar fashion, Abraham Ravish expanded the smegma theory to indict smegma as the cause of prostate cancer by travelling upstream through the urethra to invade the prostate gland. [71] Davis-Daneshfar and Trueb speculated that chronic infection with M. smegmatis is the cause of plasma cell (Zoon’s) balanitis, [72] but Yoganathan et al. could not isolate the organism in any of their cases. [73]
Some have shown an unwillingness to abandon the smegma theory. When it was postulated that sperm proteins caused cervical cancer, it was the smegma mixing with the sperm proteins that were to blame. [74] When diaphragm use was found to decrease cervical cancer, it was postulated that it provided a barrier to contact with smegma. [75] When it was clear that cervical cancer resulted from a viral infection, some still postulated that smegma was a necessary part for the viral exposure to be carcinogenic. [45] Those promoting the ‘cocoon’ theory prefer to think of smegma as a cofactor in the development of penile cancer.
There are two reasons to dismiss this speculation. First, there is no scientific evidence to support the assertion. Second, it is analogous to declaring saliva a cofactor in the development of lip cancer in those who chew tobacco. Both saliva and smegma are bodily fluids that serve a function and, like any other bodily fluid, are present in organs than can develop a malignancy. The purpose of the scientific method is to distinguish between wishful thinking, strongly held pinion, and provable fact. The smegma theory of disease, which began as wishful thinking on the part of circumcision zealots such as Abraham Wolbarst and Abraham Ravich, has evolved into irrefutable dogma, but as modern physicians, we need to recognize that, until proved otherwise, smegma is harmless.
References
69. Boczko S, Freed S. Penile carcinoma in circumcised males. N Y State J Med 1979; 79: 1903–1904.
70. Culp D. Penile cancer. J Iowa Med Soc 1973; 63: 201–202.
71. Ravich A, Ravich RA. Prophylaxis of cancer of the prostate, penis and cervix by circumcision. N Y J Med 1951; 51: 1519– 1520.
72. Davis-Daneshfar A, Trueb RM. Bowen’s disease of the glans penis (erythroplasia of Queyrat) in plasma cell balanitis. Cutis 2000; 65: 395–398.
73. Yoganathan S, Bohl TG, Mason G. Plasma cell balanitis and vulvitis (of Zoon). A study of 10 cases. J Reprod Med 1994; 39: 939–944.
74. Sandler B. Sperm basic proteins in cervical carcinogenesis. Lancet 1978; 2: 208–209.
75. Sandler B. Contraceptives and cervical carcinoma. Br Med J 1969; 1: 356–357.
Full text available from CIRP.
Why mice don't live in the foreskins of horses
The article by Boczko and Freed relied heavily on an eccentric experiment from 1947 in which A. Plaut and A. C. Kohn-Speyer tried to induce cancer in mice by doses of smegma harvested from horses. Despite persistent applications, it appears that they were successful in producing cancerous lesions in only about 60 of 400 victims, and I say “appears” because the presentation of their results is so confusing that it is very difficult to work out just what the results were. They also reported that up to 500 days the smegma-treated mice actually fared better than those who missed out: a survival rate of 47% and 30% respectively. Had they stopped the experiment at that point they would have been forced to conclude that horse smegma boosted mouse health. The most one can say about this preposterous exercise is that it explains one of the great puzzles of zoology: why mice don't live inside equine prepuces.
Plaut A, Kohn-Speyer AC. Carcinogenic action of smegma. Science 1947; 105: 391–392.
Do you like this page?