Context: Breast cancer in young women is relatively rare worldwide, with patients under the age of 35 accounting for only 2% to 25% of all women diagnosed with this cancer. The objective of this study is to describe the epidemiological, clinical and histological profile of breast cancer in patients under 40 years of age.

Methods: This is a comparative study between young and older patients at the Mohammed VI Center for Cancer Treatments. This study covered various aspects, including sociodemographic data and family history of cancer, gyneco-obstetrics, and circumstances of discovery of breast cancer, histopathological characteristics and molecular classification of breast cancer.

Results: Among the 305 patients treated, 64 were aged 40 or younger, or 20.98% of the total.
Breast cancer in our younger patients did not appear to differ significantly from that in older women, both in terms of sociodemographic factors and histopathological and molecular characteristics. The average age at first pregnancy was 23.85 years and the average parity was 1.58 children. 37.5% of young women were nulliparous. Among multiparous women, 95% breastfed their children.

The average age of menarche was 13.34 years in young patients compared to 13.30 years in older patients (p = 0.85). Among the 6 postmenopausal patients (9.3% young women), the average age of onset of menopause was 39.17 years. 59.4% of young women used oral contraceptives, compared to 60.2% of older women.
A family history of breast cancer was noted in 21.9% of young patients. The circumstances of discovery of breast cancer, most cases in both groups were identified by self-palpation or during a screening mammogram. The most common tumors were stage T2, involving lymph node invasion, and high-grade SBR II and III in 73.7% and 22.8% of cases, respectively. These were mainly invasive ductal carcinomas expressing hormonal receptors (ER and RP). About 30% were HER2+. No cases of bilateral cancer were observed in younger patients.

Conclusion: Breast cancer in young women is a significant problem in our study population and its incidence is increasing worldwide. The absence of a systematic screening program before the age of 40 may explain the aggressive behavior of tumors in this age group.