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Jessica Desamero, PhD
Recently, I noticed I knew a good number of individuals that have developed cancer while pregnant or shortly after giving birth. Although there’s no direct correlation between pregnancy and the risk of cancer, could there be an indirect link?
After researching potential causes, I found that pregnancy-associated cancer is rare but possible. Pregnancy-related factors can indirectly influence cancer development. Women are also prone to diseases that increase cancer risk. Let’s explore factors contributing to this increase in cancer risk among pregnant women:
Pregnancy-associated cancer (PAC)
Pregnancy-associated cancer (PAC) occurs in about 1 in 1,000 pregnancies (1). The most common cancers linked to pregnancy are melanoma, breast cancer, cervical cancer, lymphoma, and leukemia (2). However, incident and prevalent cancer types can vary among populations, with underrepresentation in data, especially in underdeveloped countries (2). Therefore, the actual frequency of PAC may be higher than reported. Recently, the incidence has been increasing, mainly due to mothers having children later in life, particularly in higher-income countries (1).
The pathophysiology of PAC is not fully understood, partly because identifying PAC can already be challenging. Pregnant individuals usually undergo physiological changes, which may mask the signs and symptoms of cancer. Pregnancy-associated breast cancer is particularly complex to diagnose due to the structural and functional changes the breast undergoes during pregnancy and lactation. (3) Thus, cancers may be left undiagnosed, as physicians may assume the symptoms are typical pregnancy signs. If the physicians do decide to investigate symptoms further, they may be hesitant to use common diagnostic procedures that may harm the fetus. And if physicians do use the diagnostic methods, there is always a chance the pregnancy itself may interfere with results. For example, measuring the levels of serum tumor markers is usually useful in detecting cancer, but these markers are unreliable in pregnant patients, as serum levels would already be high. Thus, diagnosing cancer during pregnancy is often delayed. (2)
One systematic review of population-based studies examined the frequency of various cancer types in diverse populations and confirmed the concerning rates of PAC. Here, researchers confirmed the overall frequency of PAC and found that most PAC cases are diagnosed postpartum rather than during pregnancy. Even with the considerable variation in cancer types and populations, PAC still complicates 1 out of every 1000 pregnancies (1). Another systematic review found that PAC significantly increases the risk of serious maternal and neonatal outcomes in patients, including blood clots in veins and maternal death (4). These studies highlight the critical need to identify PAC and understand the factors that lead to adverse outcomes, especially in those diagnosed with PAC postpartum.
General cancer risk after giving birth
Giving birth can impact a woman’s risk of developing cancer. While it may reduce the risks of certain types of cancers, it also can increase the risks of others. For example, women who have had a full-term pregnancy have reduced risks of ovarian and endometrial cancer but an increased risk of kidney cancer (5). In addition, depending on their age, some mothers face an increased cancer risk after pregnancy, while others face a lowered risk. For example, with breast cancer, women who give birth at an early age and breastfeed for a longer duration have a decreased risk of breast cancer later in life; this risk lowers as they give birth to more children. However, giving birth when older than 30 increases their risk of breast cancer. In addition, recent childbirth gives a short-term increase in breast cancer risk, which diminishes after about 10 years (6).
In one study, researchers closely reviewed past evidence on the maternal risks of several malignancies (5). In particular, they explored the role of pregnancy hormones and characteristics and how they are associated with different cancer types (Table 1). However, overall knowledge on the effects of pregnancy factors on cancer risk is still limited. They saw that results vary between studies for some pregnancy-related factors, and the effects of other factors on several cancer types are still unclear.
Table 1: Summary of a few pregnancy hormones/characteristics and how they affect cancer risk (Troisi et al., 2019).
| Hormone/characteristic | Presence and role in pregnancy | Effects on cancer risk |
| Excess progesterone | Helps maintain early pregnancy. (e.g., prepares uterus for implantation, supports developing embryo/fetus) | Increases risk of breast cancer. Decreases risk of epithelial ovarian cancer. |
| Elevated human chorionic gonadotropin (hCG) | Is produced by the placenta. Regulates fetal growth and stimulates the production of other important pregnancy hormones. | Decreases risk of breast cancer. May increase risk of thyroid cancer. |
| Preeclampsia | An uncommon but possible pregnancy complication that causes high blood pressure. | Decreases risk of breast cancer. Effects on other cancers are still unknown. |
Diseases and other factors that can affect the risk of certain cancer types
As mentioned earlier, the risk of cancer increases with age (7). Women are especially at higher risk for cancers such as breast, colorectal, lung, cervical, endometrial, ovarian, and skin cancer (8).
Certain conditions, like autoimmune disease, 2) endometriosis, and 3) polycystic ovary syndrome, can also increase cancer risk in women.
Autoimmune disease
In autoimmune diseases, the immune system is overactive and mistakenly attacks yourbody. One of the most prevalent autoimmune diseases is Rheumatoid Arthritis (RA), which primarily causes pain, swelling, and inflammation in the joints. Previous population-based studies observed cancer rates among large cohorts of patients with RA (9). They found that RA increased the risk of several malignancies, particularly non-Hodgkin lymphoma, a blood cancer that develops in the lymphatic system. The chronic inflammation commonly seen in autoimmune diseases seems to be a main contributing factor to the increased risk of cancers like lymphoma and leukemia, as this can promote cancer cell and tumor growth.
Endometriosis
In endometriosis, cells similar to the uterine lining grow outside of the uterus, which can cause severe pain in the pelvis. Researchers recently found that the risk of ovarian cancer is 4 times higher in women with endometriosis than in those without. Moreover, women with certain subtypes of severe endometriosis had over 9 times the risk (10). Future studies are needed to address how different endometriosis subtypes exactly promote ovarian cancer.
Polycystic ovary syndrome (PCOS)
PCOS involves reproductive hormone imbalance and can cause a range of health issues. PCOS has been found to increase the risk of endometrial cancer (11). Several medical conditions associated with PCOS can contribute to this increased risk. For example, ovulation irregularities and a chronic absence of ovulation can both cause the lining of the uterus to thicken abnormally due to an excess number of cells; this can possibly progress to endometrial carcinoma. The correlation between PCOS and ovarian carcinoma remains unclear (11).
Learning more about the relationship between pregnancy and cancer
In summary, several possibilities can explain why pregnancy leads to cancer in some women. It could be PAC, or it could be the increased cancer risk generally associated with certain pregnancy factors. In addition, women with autoimmune disease, endometriosis, or PCOS are at an even greater risk for certain cancers. However, the connections between pregnancy and cancer are still not fully understood. One reason is that PAC and other uncommon diseases affecting women have unfortunately not been studied as much.
Future directions could include uncovering the molecular origins of the above conditions and developing more advanced tools for cancer diagnosis that are less harmful and more accurate. With a fuller understanding, mothers would be better informed about their physiological state. And with more reliable and safe diagnostic tools, PAC can be identified earlier, which is important to treat PAC and prevent as many adverse outcomes as possible.
Header Image Source: https://www.pikrepo.com/en/free-photo-zlcdd
Edited by Joycelyn Ghansah
References
1. Dalmartello, M., Negri, E., La Vecchia, C., Scarfone, G., Buonomo, B., Peccatori, F. A., & Parazzini, F. (2020). Frequency of Pregnancy-Associated Cancer: A Systematic Review of Population-Based Studies. Cancers, 12(6), Article 6. https://doi.org/10.3390/cancers12061356
2. Hepner, A., Negrini, D., Hase, E. A., Exman, P., Testa, L., Trinconi, A. F., Filassi, J. R., Francisco, R. P. V., Zugaib, M., O’Connor, T. L., & Martin, M. G. (2019). Cancer During Pregnancy: The Oncologist Overview. World Journal of Oncology, 10(1), 28–34. https://doi.org/10.14740/wjon1177
3. Galati, F., Magri, V., Arias-Cadena, P. A., Moffa, G., Rizzo, V., Pasculli, M., Botticelli, A., & Pediconi, F. (2023). Pregnancy-Associated Breast Cancer: A Diagnostic and Therapeutic Challenge. Diagnostics, 13(4), 604. https://doi.org/10.3390/diagnostics13040604
4. Walters, B., Midwinter, I., Chew-Graham, C. A., Jordan, K. P., Sharma, G., Chappell, L. C., Crosbie, E. J., Parwani, P., Mamas, M. A., & Wu, P. (2024). Pregnancy-Associated Cancer: A Systematic Review and Meta-Analysis. Mayo Clinic Proceedings: Innovations, Quality & Outcomes, 8(2), 188–199. https://doi.org/10.1016/j.mayocpiqo.2024.02.002
5. Troisi, R., Bjørge, T., Gissler, M., Grotmol, T., Kitahara, C. M., Sæther, S. M. M., Ording, A. G., Sköld, C., Sørensen, H. T., Trabert, B., & Glimelius, I. (2018). The Role of Pregnancy, Perinatal Factors, and Hormones in Maternal Cancer Risk: A review of the evidence. Journal of Internal Medicine, 283(5), 430–445. https://doi.org/10.1111/joim.12747
6. Reproductive History and Cancer Risk—NCI (nciglobal,ncienterprise). (2016, November 30). [cgvArticle]. https://www.cancer.gov/about-cancer/causes-prevention/risk/hormones/reproductive-history-fact-sheet
7. Risk Factors: Age – NCI (nciglobal,ncienterprise). (2015, April 29). [cgvArticle]. https://www.cancer.gov/about-cancer/causes-prevention/risk/age
8. Cancer Facts for Women | Most Common Cancers in Women. (n.d.). Retrieved June 15, 2025, from https://www.cancer.org/cancer/risk-prevention/understanding-cancer-risk/cancer-facts/cancer-facts-for-women.html
9. Ehrenfeld, M. (2013). Autoimmune diseases and cancer. In Autoimmunity: From Bench to Bedside [Internet]. El Rosario University Press. https://www.ncbi.nlm.nih.gov/books/NBK459441/
10. Endometriosis types and ovarian cancer risk | National Institutes of Health (NIH). (n.d.). Retrieved June 18, 2025, from https://www.nih.gov/news-events/nih-research-matters/endometriosis-types-ovarian-cancer-risk
11. Shetty, C., Rizvi, S. M. H. A., Sharaf, J., Williams, K.-A. D., Tariq, M., Acharekar, M. V., Guerrero Saldivia, S. E., Unnikrishnan, S. N., Chavarria, Y. Y., Akindele, A. O., Jalkh, A. P. C., Eastmond, A. K., & Hamid, P. (n.d.). Risk of Gynecological Cancers in Women With Polycystic Ovary Syndrome and the Pathophysiology of Association. Cureus, 15(4), e37266. https://doi.org/10.7759/cureus.37266
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