Lack of effectiveness of CO2 cryotherapy for treatment of CIN

Cervical Precancer Treatment in Low- and Middle-Income Countries: A Technology Overview

Cervical cancer is the fourth leading cause of cancer-related death in women worldwide, with 90% of cases occurring in low- and middle-income countries (LMICs). There has been a global effort to increase access to affordable screening in these settings; however, a corresponding increase in availability of effective and inexpensive treatment modalities for ablating or excising precancerous lesions is also needed to decrease mortality. This article reviews the current landscape of available and developing technologies for treatment of cervical precancer in LMICs. At present, the standard treatment of most precancerous lesions in LMICs is gas-based cryotherapy. This low-cost, effective technology is an expedient treatment in many areas; however, obtaining and transporting gas is often difficult, and unwieldy gas tanks are not conducive to mobile health campaigns. There are several promising ablative technologies in development that are gasless or require less gas than conventional cryotherapy. Although further evaluation of the efficacy and cost-effectiveness is needed, several of these technologies are safe and can now be implemented in LMICs. Nonsurgical therapies, such as therapeutic vaccines, antivirals, and topical applications, are also promising, but most remain in early-stage trials. The establishment of evidence-based standardized protocols for available treatments and the development and introduction of novel technologies are necessary steps in overcoming barriers to treatment in LMICs and decreasing the global burden of cervical cancer. Guidance from WHO on emerging treatment technologies is also needed.

Effectiveness of cryotherapy treatment for cervical intraepithelial neoplasia

OBJECTIVE

To assess the effectiveness of cryotherapy treatment delivered by general practitioners in primary care settings, as part of a screen-and-treat approach for cervical cancer prevention.

METHOD

Women aged between 25 and 49 years residing in San Martin, Peru, who were positive on visual inspection screening were treated, if eligible, with cryotherapy following biopsy. At 12 months post cryotherapy treatment the participants were evaluated for treatment effectiveness and examined by visual inspection and Papanicolaou test and, if positive, referred to a gynecologist for colposcopy and biopsy.

RESULTS

Cryotherapy treatment was performed for 1398 women; of these, 531 (38%) had a histology result of cervical intraepithelial neoplasia (CIN). Cryotherapy effectively cured CIN in 418 (88%) women, including 49 (70%) women with a baseline diagnosis of CIN 3.

CONCLUSION

Cryotherapy is an effective treatment for cervical precancerous lesions; it can easily be administered by general practitioners in primary care settings following visual inspection screening.

Effect of cough technique and cryogen gas on temperatures achieved during simulated cryotherapy

BACKGROUND

Cryotherapy is often used to treat cervical precancer in developing countries. There are different methods and cryogen gases used for cryotherapy, including the freeze-flush-freeze (cough) technique employed to minimize gas blockage. However, there is limited information to compare their effectiveness.

METHODS

Using a tissue model, we compared temperature-time curves for four cryotherapy methods: uninterrupted freezing with nitrous oxide (N2O) and carbon dioxide (CO2), and two methods using a standard and extended version of the cough technique with CO2.

RESULTS

Uninterrupted freezing with both N2O and CO2 produced tissue temperatures less than -20 degrees C (-40 degrees C and -30 degrees C respectively). CO2 cryotherapy procedures using the two cough techniques produced temperatures greater than -20 degrees C in the model tissue.

CONCLUSION

CO2 cryotherapy using the cough technique may not achieve sufficiently low temperatures to produce the desired therapeutic effect. Other alternatives to the prevention of gas blockage should be developed.

Comparison of depth of necrosis achieved by CO2- and N2O-cryotherapy

OBJECTIVE

To compare the depth of necrosis achieved using CO2- and N2O-cryotherapy.

METHOD

We treated 20 women with CO2-cryotherapy and 20 with N2O-cryotherapy 24 h prior to undergoing total hysterectomy for reasons unrelated to cervical cancer. Depth of necrosis in the ectocervix was measured on surgically removed tissue.

RESULTS

The mean depth of necrosis for the anterior lip achieved by N2O-cryotherapy was 5.3 mm compared with 3.4 mm by CO2-cryotherapy (P<0.001). We found similar results for the posterior lip (5.0 vs 3.1 mm; P<0.001). N2O-cryotherapy was more likely than CO2-cryotherapy to achieve a depth of necrosis of >or=4.8 mm for the anterior lip (75% vs 15%; P<0.001) and posterior lip (60% vs 5%; P<0.001).

CONCLUSIONS

Our study showed that CO2-cryotherapy may not achieve the depth of necrosis necessary to completely destroy cervical precancer and therefore may be less robust than N2O-cryotherapy.

Human papillomavirus and cervical cancer

Cervical cancer is the second most common cancer in women worldwide, and knowledge regarding its cause and pathogenesis is expanding rapidly. Persistent infection with one of about 15 genotypes of carcinogenic human papillomavirus (HPV) causes almost all cases. There are four major steps in cervical cancer development: infection of metaplastic epithelium at the cervical transformation zone, viral persistence, progression of persistently infected epithelium to cervical precancer, and invasion through the basement membrane of the epithelium. Infection is extremely common in young women in their first decade of sexual activity. Persistent infections and precancer are established, typically within 5-10 years, from less than 10% of new infections. Invasive cancer arises over many years, even decades, in a minority of women with precancer, with a peak or plateau in risk at about 35-55 years of age. Each genotype of HPV acts as an independent infection, with differing carcinogenic risks linked to evolutionary species. Our understanding has led to improved prevention and clinical management strategies, including improved screening tests and vaccines. The new HPV-oriented model of cervical carcinogenesis should gradually replace older morphological models based only on cytology and histology. If applied wisely, HPV-related technology can minimise the incidence of cervical cancer, and the morbidity and mortality it causes, even in low-resource settings.

Preliminary report of a gas conditioner to improve operational reliability of cryotherapy in developing countries

Background

Cryotherapy is a safe, affordable, and effective method of treatment for cervical intraepithelial neoplasia. In some low-resource settings, environmental conditions or qualities of the refrigerant gas can lead to blockage of cryotherapy equipment, terminating treatment. A prototype of a gas conditioner to prevent operational failure was designed, built, and field tested.

Methods

The prototype conditioner device consists of an expansion chamber that filters and dries the refrigerant gas. Users in Peru and Kenya reported on their experience with the prototype conditioner. In Ghana, simulated cryotherapy procedures were used to test the effects of the prototype conditioner, as well as the commonly used "cough technique."

Results

Anecdotal reports from field use of the device were favorable. During simulated cryotherapy, the prevalence of blockage during freezing were 0% (0/25) with the device alone, 23.3% (7/30) with the cough technique alone, 5.9% (1/17) with both, and 55.2% (16/29) with neither (Pearson's Chi square = 26.6, df = 3, p < 0.001 (comparison amongst all groups)).

Conclusion

This prototype design of a cryotherapy gas conditioner is a potential solution for low-resource settings that are experiencing cryotherapy device malfunction.