Biomedical Engineering Reference
In-Depth Information
Vona-Davis and Rose, 2007). Obesity has been associated with breast cancer
risk (Chlebowski, 2005). Because adipose tissue secretes estrogens, the mechan-
ism through which it acts may be by accumulation of excess estrogen (Deroo
and Korach, 2006).
Breast tissue is exquisitely sensitive to the hormonal changes of early preg-
nancy (Leslie and Lange, 2005) . Many women report breast tenderness as a
first sign of pregnancy. The human breast is capable of lactation from 16 weeks
post-fertilization, with differing rates of growth and breast development before
and after parturition (Lawrence and Lawrence, 1985). During the first trimester
of pregnancy, mammary epithelial cells proliferate and duct cells branch in
response to estrogen (Sternlicht, 2006). The breast duct epithelium proliferates
into the breast fat pads where end buds develop into secretory alveoli in
response to human placental lactogen (somatomammotropin), human chorio-
nic gonadotropin, and prolactin (Harrison and Biswas, 1980; Parmar and
Cunha, 2004; Riordan, 2005). While progesterone stimulates an increase in
the size of the lobes and lobules, somatotropin and ACTH interact with
prolactin and progesterone fostering mammogenesis. During the second trime-
ster, there is further enlargement of the duct system and additional growth of
the lobules. At approximately 12 weeks, a secretory substance that is similar to
colostrum becomes visible in the acini. Subsequent prolactin production from
the anterior pituitary together with placental lactogen triggers mammary alveo-
lar differentiation, followed by the glandular secretion of colostrum. The alveoli
then become distended with colostrum (Buhimschi, 2004). The dozen or so
lactiferous sinuses radiate from the areola, draining into the nipple.
4 Cancer as a Microcosm of Embryogenesis
Most cancer cells divide rapidly and can be grown indefinitely in culture as
immortal cells, just as do embryonic stem cells. Embryonal carcinomas and
teratocarcinomas are tumors derived from embryonic cells and can differentiate
and give rise to cells of many lineages. In 1976 Beatrice Mintz and Ralph
Brinster independently showed teratocarcinomas could give rise to normal
chimeric mice (Brinster, 1976; Mintz and Illmensee, 1975).
4.1 Soil and Seed
In 1889, the English physician Stephen Paget introduced the ''soil and seed''
hypothesis of metastasis to English-speaking medicine, by crediting the idea to
Fuchs (Fuchs, 1882). In Paget's study of 735 fatal cases of breast cancer, he
concludes that the distribution of metastases cannot be due to chance alone and
that different tissues provide optimal conditions for the growth of specific
cancers. He noticed that patients with primary breast cancers had secondary
