你说的没科学数据支持。实际上美国从1940-1980 发病率是上升的，这我想主要是人的寿命在这段时间逐渐增长，而乳腺癌

在老年的发病率高造成了整体的发病率高（ 如果象原始社会人均寿命30岁人还没来得及得癌就死掉了肯定发病率低). 1980-200 可能是更年期综合症激素治疗导致乳腺癌增加。 但在2000年后下降了，以后一直比较稳定，没上升。
http://ww5.komen.org/BreastCancer/Statistics.html

Breast cancer incidence over time From the 1940s until the 1980s, breast cancer incidence (new cases) rates in the U.S. increased by a little over one percent each year. In the 1980s, incidence rose greatly (likely due to increased mammography screening), and then leveled off during the 1990s [41].

The incidence of breast cancer declined in the early 2000s [37-38]. Although mammography screening rates fell somewhat over this same time period, studies show these changes were not likely related to the decline in breast cancer rates [42-43]. The decline appears to be related to the drop in use of menopausal hormone therapy (postmenopausal hormone use) that occurred after the Women's Health Initiative study showed its use increased the risk of breast cancer [37,41-43].

Since 2004, the incidence of breast cancer has remained stable [38].

- See more at: http://ww5.komen.org/BreastCancer/Statistics.html#sthash.0HSlCwfG.dpuf
你还可到下面这个网页看一下统计分析图，从1992-2011 发病率基本稳定，只是2000年前略有上升，然后马上又降下来了。死亡率从1992-2011 整体是下降的。

http://seer.cancer.gov/statfacts/html/breast.html

还有这篇文章
Breast Cancer Statistics, 2013
http://onlinelibrary.wiley.com/doi/10.3322/caac.21203/pdf

再看一下这一个，http://www.cancer.org/acs/groups/content/@research/documents/document/acspc-042725.pdf
从1975 到2010， 0-49岁年龄段非常稳定不升，与你说的年轻化不符。另外所有年龄放在一起统计1975-1987略有上升，以后增加也不明显。但50岁以上的单独分析1975-2000年增加，然后下降(page 6, figure 4b)。增加主要是由于寿命的增加导致发病率增加，这个统计里也有图表说明（见第2页figure 1)，还有可能与那个时期更年期综合症激素治疗有关。 死亡率1975-1995 是上生的，以后大幅下降（page 7, figure 5b)

总之，你的 “有越研究越高发，越研究越发病年轻化之势” 没有充分的统计数据支持。