Pregnancy and risk of cancer recurrence

Does pregnancy increase the risk or delay the diagnosis of cancer recurrence for women with a history of breast cancer?

A meta-analysis of 14 studies performed by Azim et al. observed that women who became pregnant following breast cancer diagnosis had a 41% reduced risk of death compared to survivors who did not become pregnant [PRR: 0.59 (95% confidence interval (CI): 0.50–0.70)]. This difference was seen irrespective of the type of the study and particularly in women with history of node-negative disease. In a subgroup analysis, the outcome of women with history of breast cancer who became pregnant was compared to breast cancer patients who did not get pregnant and were known to be free of relapse. In this analysis, there was no significant difference in survival between the groups [PRR: 0.85; 95% CI: 0.53–1.35].[1]

A more recent meta-analysis by Hartmen et al. found that women who become pregnant after a breast cancer diagnosis have a significantly reduced risk of death compared to those who do not become pregnant [pHR 0.63; 95 % CI 0.51-0.79]. Additional analysis to account for the "healthy mother effect" generated similar results [pHR 0.65; 95 % CI 0.52-0.81].[2]

A case-control study of over 1,000 breast cancer patients performed by Lambertini et al. did not identify pregnancy as a risk factor for disease recurrence. At a median follow-up of 7.2 years after pregnancy, no difference in disease-free survival was observed between pregnant and non-pregnant patients with ER-positive (HR = 0.94, 95% CI = 0.70 to 1.26, P = 0.68) or ER-negative (HR = 0.75, 95% CI = 0.53 to 1.06, P = 0.10) disease.[3] This supported results from an earlier study of over 10,000 breast cancer survivors that found that women who had a full-term pregnancy after breast cancer treatment had a reduced risk of dying (relative risk: 0.73; 95% confidence interval: 0.54-0.99) compared to other women with breast cancer.[4]

A more recent study of over 30,000 Korean women treated for breast cancer has further strengthened the evidence. Lee et al. found that women who became pregnant after breast cancer did not have a different risk of recurrence (hazard ratio [HR], 0.503; 95% confidence interval [CI], 0.434 to 0.584) and death (HR, 0.520; 95% CI, 0.397 to 0.681), compared with those who did not become pregnant after breast cancer treatment.[5]

Evidence Summary One

Recommendation One

Does pregnancy increase the risk or delay the diagnosis of cancer recurrence for women with a history of cancer?

Pregnancy induces wide-ranging physiological changes, and all body systems are in some way affected by the pregnant state. These include changes to haematological parameters and the immune and hormonal environments. Additionally, there is the possibility that pregnancy may delay the diagnosis of cancer recurrence, either because of clinical reluctance to perform investigations that would permit diagnosis (or the optimal investigations are unsafe or impractical in pregnancy), or because the symptoms and signs suggestive of recurrence might be ascribed to or masked by pregnancy.

There is limited literature on the impact of pregnancy on disease recurrence for cancers other than in breast cancer. Byrom et al. published a meta-analysis on the impact of pregnancy on melanoma mortality and recurrence and found no significant effect of subsequent pregnancy on melanoma mortality after 11 to 20 years of follow-up (pooled HR, 0.81; 95% CI 0.60–1.09) and no significant differences in melanoma recurrence.^[6] The most recent of the papers found that women who had post-cancer pregnancies the risk of cause-specific death was significantly decreased^[7] and pregnancy status after diagnosis of melanoma was not a significant predictor of survival (hazard ratio for death in women who had pregnancy subsequent to the diagnosis of melanoma was 0.58; 95% CI, 0.32 to 1.05).^[8]

A cohort study by Weibull et al. investigated whether there is an association between pregnancy and relapse in women with Hodgkin lymphoma. The adjusted HR for the comparison of the pregnancy-associated relapse rate to the non–pregnancy-associated relapse rate was 0.29 (95% CI, 0.04 to 2.18). The expected number of relapses in women with a recent pregnancy, given that they would experience the same relapse rate as that of women without a recent pregnancy, was 3.76; the observed-to-expected ratio was 0.27 (95% exact CI, 0.01 to 1.51).^[9] A smaller study found no evidence that pregnancy increases the recurrence rate among women in remission from Hodgkin lymphoma.^[10]

Evidence Summary Two

Recommendation Two