Fig. 1

Molecular subtypes of the PABC, breast cancer other than PABC, PABC developed in women’s first pregnancy and non-first pregnancy. a Molecular subtypes of the PABC, n = 203. b Molecular subtypes of breast cancer other than PABC (non-PABC), n = 43,721. c Molecular subtypes of the PABC developed in women’s first pregnancy (First-Pregnancy subgroup), n = 79. d Molecular subtypes of the PABC not developed in women’s first pregnancy (Non-First-Pregnancy subgroup), n = 124. The P value was less than 0.001, by using Pearson Chi-square tests to compare the distribution of molecular subtypes in PABC patients (a) and non-PABC patients (b), demonstrating a difference. The P value was 0.554, by using Pearson Chi-square tests to compare the distribution of molecular subtypes in First-pregnancy group (c) and Non-first-pregnancy group (d), demonstrating no statistical significance. PABC=Pregnancy-associated breast cancer; ER = Estrogen Receptor; PR = Progesterone Receptor; HER-2 = Human Epidermal Growth Factor Receptor-2, HR (Hormone Receptor) +: Either ER or PR+. Luminal A: ER+, PR+, HER-2 (−), Ki-67 < 14%; Luminal B: HR+, Ki-67 ≥ 14%; HR+, HER-2(+); ER+, PR-; Her-2 overexpression: HR (−), HER-2 (+); TNBC (Triple negative breast cancer): ER (−), PR (−), HER-2 (−)