Safety of pregnancy following breast cancer

To the Editor

We appreciate the comments by Peccatori and Azim regarding our recent publication [1] in Acta Oncologica. We agree with their fundamental point. A subsequent full term pregnancy may well have a beneficial effect on the risk of relapse in patients with early breast cancer. For several reasons we however up-front decided not to perform the subgroup analysis analyses on hormone receptor status that Peccatori and Azim are suggesting. First of all the power of subgroup analysis would be small even in this large cohort, secondly shifting methodologies have been used for oestrogen and progesterone receptor measurements over the more than two decades [2].

The relative importance of pregnancy associated hormonal changes is not fully understood, e.g., the role of prolactin and insulin and other receptors e.g. the insulin-like growth factor I receptor may be important [3], [4]. Based on our incomplete understanding of a possible “biological” effect and a genuine concern regarding the risk of selection bias we want to avoid the promotion of pregnancy as therapeutic measure in breast cancer patients. Furthermore, it is important to bear in mind, that the risk estimates tells us about differences in survival between groups of women with breast cancer. Women with a history of breast cancer will overall still have an increased risk of death compared with other healthy mothers. The present study only indicates that a pregnancy after treatment for breast cancer has no negative impact on the prognosis.