Discovering Ovarian Cancer Biomarkers Through Innovative Breath Analysis

Introduction – Ovarian Cancer

Ovarian cancer is the sixth most common cancer worldwide among women in developed countries and the ninth in developing countries. Unfortunately, of the 225,000 women worldwide who are diagnosed with ovarian cancer annually, 140,200 die from the disease (1). Symptoms can occur at all stages, however, they are usually nonspecific and can also occur in females without ovarian cancer.

The serum biomarker cancer antigen 125 (CA125) is widely used across the globe as a biomarker for ovarian cancer in symptomatic females (2). CA125 is a protein found on the surface of ovarian cancer cells and on some normal cells, meaning that females with ovarian cancer often have a high level of CA125 in their blood.

However, a high level of CA125 in the blood can also be a sign of conditions such as endometriosis (3) and pregnancy (4), as well as other cancers (5). For example, one study looked at 50,000 women who had seen their doctor and took the CA125 test for ovarian cancer. This study found that 10% of women with high levels of CA125 were diagnosed with ovarian cancer, however, 380 women with an abnormal CA125 result had another type of cancer such as lung, pancreatic, or bowel cancer (6). This highlights a need for more specific and sensitive biomarkers and diagnostic tests for ovarian cancer.

Other diagnostic tests for ovarian cancer are available such as transvaginal ultrasound, however, these techniques are invasive and uncomfortable for patients. Also, more than 70% of patients are diagnosed at the advanced stages of the disease (stage 3/stage 4) and have a 5-year survival rate of less than 30%. When ovarian cancer is detected in its early stages, it increases the 5-year survival rate to 85-90% (7).

There is therefore a need for non-invasive diagnostic techniques and biomarkers for the early detection of ovarian cancer. A study by Amal et al (8) evaluated the ability to detect and classify ovarian cancer from exhaled breath samples non-invasively.

Methods

Exhaled breath samples were collected from 48 patients with ovarian cancer (25 patients with early-stage ovarian cancer, 22 patients with advanced stage ovarian cancer, and 1 patient with an unknown stage), 86 patients with benign genital tract neoplasia (BGN), and 48 tumor-free controls. Two breath samples were collected from each participant, and the inhaled ambient air was filtered. Ambient air samples were also collected and analyzed for comparison with breath samples.

The breath samples were analyzed using gas-chromatography linked with mass-spectrometry (GC-MS) to determine their volatile organic compound (VOC) composition.

Results

A total of 133 different VOCs were found in the exhaled breath samples, with 96 of these VOCs found in more than 85% of samples. 56 VOCs had a spectral match based on the library provided by the National Institute of Standards and Technology (NIST) were left to be analyzed.

Two VOCs were found to significantly discriminate between ovarian cancer participants from the non-cancer groups. These VOCs were decanal and 2-butanone which were found in higher levels in ovarian cancer breath samples than in the non-cancer group’s breath samples (decanal p-value = 0.005 and 2-butanone p-value = 0.007).

Nonanal, styrene, and hexadecane were found in higher concentrations in ovarian cancer breath samples than the tumor-free controls (nonanal p-value = 0.036, styrene p-value = 0.011, hexadecane p-value = 0.028). No significant VOCs were found when comparing early and advanced stage ovarian cancer.

Table 1. VOCs from exhaled breath samples identified in patients with ovarian cancer (p-value < 0.05)

Discussion

These results highlight that cancer could have a unique VOC signature detectable in exhaled breath. Two of the significant VOCs identified in this study belong to the aldehyde family – decanal and nonanal. Aldehydes in the breath have both endogenous and exogenous sources. One endogenous source could be that in ovarian cancer cells, ALDH1L1 (an enzyme that breaks down aldehydes) is downregulated, which can lead to increased aldehyde levels (9), which could explain the raised levels seen in this study.

Hexadecane was also found in higher levels in ovarian cancer patients. Hexadecane is related to the alkane chemical group, and one way that alkanes and hydrocarbons are produced in the body is through oxidative stress. Alkanes are predominantly produced by the peroxidation of unsaturated fatty acids by reactive oxygen species. Therefore, elevated levels of hexadecane in ovarian cancer exhaled breath samples could be related to the increase in oxidative stress seen in cancer.

VOCs found in exhaled breath could therefore be used as non-invasive biomarkers for ovarian cancer, to be used alongside currently used biomarkers such as CA125. Our Breath Biopsy Collection Station, including the ReCIVA® Breath Sampler and the CASPER® Portable Air Supply enables reliable and reproducible collection of breath VOCs.

Decanal and nonanal are both found in the Breath Biopsy VOC Atlas®, a catalog of identified and quantified VOCs found in exhaled breath. The Atlas also provides insight and scientific context to identified compounds to enable the confident selection of candidate biomarkers for a variety of diseases, including cancer. Sign up here to gain exclusive access to the Atlas. Owlstone Medical can therefore support high-resolution targeted and untargeted breath analysis for biomarker discovery.

References

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3. Muyldermans M, Cornillie FJ, Koninckx PR. CA125 and endometriosis. Hum Reprod Update. 1995 Mar;1(2):173–87. doi: 10.1093/humupd/1.2.173
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