Breast cancer in young women. Aspects of heredity and contralateral disease

Sammanfattning: Breast cancer is the most commonly diagnosed cancer among women in Sweden, as well as worldwide. In Sweden, 8,288 women were diagnosed with invasive breast cancer in 2019, out of whom approximately 1.5% were younger than 35 years of age. Although breast cancer is relatively uncommon in young women, they tend to be diagnosed with more aggressive tumors at a more advanced stage, and have a poorer prognosis compared with older women. Young patients are also more likely to harbor a strong genetic predisposition for breast cancer.In paper I–III, women who were diagnosed with breast cancer at an age of 35 years or younger in the South Swedish Health Care Region were studied. In paper I, the concordance between self- and register-reported information regarding first-degree family history of cancer was evaluated. Almost perfect agreement between reports of family history of breast and ovarian cancers, but lesser agreement for other types of cancer, was observed. In addition, the frequencies of carriers and noncarriers of pathogenic variants and tumor characteristics for each of these group were described. Pathogenic variants were identified in BRCA1 (19%), BRCA2 (7%), and other genes, i.e., TP53, CHEK2, and PALB2 (4.5%). Compared with other groups, women with pathogenic variants in BRCA1 were more likely to be diagnosed with high grade, estrogen receptor-, progesterone receptor-, and triple-negative tumors. We also noted that even though all included women fulfilled the criteria for consideration of genetic counseling and testing, many had not been referred to the Oncogenetic Clinic in Lund. In paper II, we subsequently observed that both place of residence at breast cancer diagnosis and treating hospital were associated with the probability for a referral for genetic counseling and testing, and in paper III, most women stated that the main reason for not undergoing genetic testing when they were first diagnosed with breast cancer was that they had not received any information about genetic counseling and testing from their treating physicians.Among women who have previously been diagnosed with breast cancer, both young age and the identification of a pathogenic variant are associated with an increased risk for the development of a new primary breast cancer. The second breast cancer can occur ipsilaterally, i.e., in the same breast, but most occur in the contralateral breast. In paper IV, we evaluated how the incidence of contralateral breast cancer (CBC) has evolved in Sweden since the 1960s. A statistically significant increase in CBC incidence, within ten years from the first breast cancer diagnosis between the 1960s and 1980s, was observed. This increase was seen throughout all age groups, with the steepest increase in women younger than 40 years. However, a subsequent significant decrease in the incidence of invasive CBCs after the 1980s was also seen, in contrast to in situ CBCs, where the incidence stabilized in the years after.In paper III, a Traceback approach, i.e., a retrospective genetic outreach activity, was also evaluated by inviting all the women diagnosed with early-onset breast cancer, who had not previously been referred for genetic counseling, to an analysis of breast cancer predisposing genes. Pathogenic variants were identified in BRCA1 (n=2), CHEK2 (n=1), and ATM (n=1), i.e., in four (14%) of the participants. The Traceback pilot study procedure, with written pre-test information and genetic testing, followed by in-person counseling for carriers of pathogenic variants only, was well accepted. Based on these results, we will initiate an enlarged Traceback study were all previously untested women diagnosed with breast cancer between the ages of 36 and 40 years will be invited.