It has been widely studied how age at diagnosis relates to survival in breast cancer. Studies have shown that breast cancer patients with a younger age are more likely to develop malignancy and have a poor prognosis [20, 21]. Although older women have inert tumors in breast cancer [22], they have a poor prognosis of breast cancer under treatment or overtreatment [23]. Therefore, breast cancer prognosis has been controversial based on the age at diagnosis.
In our study, we explored the relationship between diagnosis age and OS、BCSS and DFS. Outcomes showed that breast cancer patients age level in Q2 had a higher survival than in Q1, Q3 and Q4 patients in our study. There have been numerous studies showing a pattern between the age at diagnosis and OS, BCSS and DFS in breast cancer.
For OS, one study has shown a significantly higher 10-year OS for breast cancer patients ≥ 40 years than those < 40 years [24]. However, in another study, there was no statistically significant difference in 5-year OS between the two [25]. It may be due to the shorter follow-up period. According to the study by Wong et al, age at diagnosis was U-shaped in relation to OS with a minimum age of 45 years [26]. In our study, diagnosis age and OS had a U-shaped relationship with the lowest of age 44 years, which is consistent with the findings of the Wong’s study. Both showed that OS decreases and then increases with age in breast cancer patients. And there was an increasing risk of competing background mortality after the lowest age, which contributed to overall survival in a greater way than breast cancer mortality alone. Our study showed that Q2 had a higher OS than in Q1, Q3 and Q4 patients. Whose age was 44–50 years, which is almost consistent with the findings of the 7-group study by Chen et al, in which patients aged 40–49 years had a significantly better OS than other groups of patients [27]. However, OS were non-significantly higher in Q1compared with Q2, which may be due to the short follow-up period in our study, resulting in a failure of statistical difference between the two.
For BCSS, some studies have indicated that breast cancer patients with a younger age have poor BCSS [28–30]. A nonlinear relationship between age and BCSS in Wong et al, the risk of dying from breast cancer was highest in the youngest patients, and this hazard decreased linearly at a rate of 5% per year with increasing age (95% CI = 2%-8%; P = 0.001) [26]. The risk of dying from breast cancer tends to be low and flat until the age at diagnosis is approximately 50 years. In our study, age and BCSS were in a U-shaped relationship. The study displayed that BCSS decreases with age until the age of diagnosis is 37 years and then shows an increase in breast cancer patients. The different findings of the two studies may be due to the fact that most patients with mastectomy in our study compared to the above study. Another study showed that patients aged 60–69 years had best BCSS among patients in other groups [27]. However, our study showed that 44–50 years had better BCSS, and BCSS were non-significantly higher in Q3 compared with Q2 in our study. There is a possibility that our study has a small sample size since it is a single-center study.
For DFS, younger breast cancer patients have worse DFS than older patients [31, 32]. Studies showed significantly lower survival with DFS in breast cancer patients < 40 years than patients ≥ 40 years [24, 33]. One study showed an association between age and the formation of an L-shape in DFS [26]. The study has shown that the older the age at diagnosis, the lower the risk of recurrence or death from breast cancer. The initial risk decreases rapidly with increasing age at presentation, suggesting that beyond approximately 40 years of age, the effect of age on breast cancer recurrence or death diminishes. In our study, however, age at diagnosis and DFS formed a U-shaped relationship. The initial risk decreases rapidly with increasing age at onset, with the curve showing the lowest value of this risk at approximately 41 years of age. this risk gradually increases with increasing age at onset after 41 years of age. And DFS rates was 13.66% (144 patients). Our result differed from Wong et al, possibly due to the inclusion of patients who were all breast-conserving patients in their study. Breast-conserving patients are generally younger, so an L-shape of age at diagnosis and DFS was observed. It May be due to different characteristics of the onset population, too.
Our study showed that patients in the intermediate age (Q2) group had better survival compared to patients in the higher (Q3、Q4) and lower (Q1) age groups. Therefore, it suggests that we should not neglect the treatment of the last two. For lower age patients, the prognosis is poorer due to the bad biological behavior of the tumor at the diagnosis time. And in the higher age patients, who often refuse standard treatment due to their poor health status, lower treatment acceptance or fear of poor tolerance to toxicity, such patients often do not receive standardized treatment leading to poor prognosis as well. The results of our study also confirm this phenomenon. For the higher age quartile, patients had a significantly higher PR-negative tumors and mastectomy rate. In contrast, KI67 levels and adjuvant chemotherapy were significantly lower among the higher age quartile than among the lower quartile. One study showed that OS rates were not lower for young patients, despite their tumors and poorer prognosis, results that patients may have benefitted from more aggressive treatment [34, 35]. Another study has shown that women over 65 years of age with T3N0M0 can benefit from radiotherapy in terms of OS and BCSS [36]. However, patients aged 18–45 years with and without radiotherapy did not have different survival times. Therefore, for both groups of patients, clinical treatment plans should be individualized to improve their late survival.
Our study is based on data information from 1054 and is part of a large sample research center. However, it has several limitations. First, the median follow-up time in the study was only 4.86 years, which is not long enough. Second, the study used a retrospective data, which may have introduced sampling bias. Finally, it belongs to a monocentric study. These above may have unknown potential impact on our findings.