Breasts (5 page)

I have heard a good anatomist say, “the breast is so complicated that I can make nothing clear of it.”

— SIR ASTLEY PASTON COOPER,
On the Anatomy of the Breast

I
N ANTIQUITY, A TEMPLE ON THE ISLAND OF RHODES DISPLAYED
a goblet said to be molded from the perfect breasts of Helen of Troy. Her face may have launched a thousand ships, but it was her breasts that really buoyed the army. In the Middle Ages, French King Henry II reportedly had casts made of the “apple-like” breasts of his mistress Diane de Poitiers for his wine cups. Marie-Antoinette’s breasts were believed to inspire the design of shallow French champagne coupes (not the narrow fluted ones, heavens), as well as of some celebrated porcelain milk bowls made by Sèvres.
¹

Some people are just born with the blueprints for a great pair of knockers. It all has to do with a magic ratio of ligaments to fat to glands. Human breast tissue falls into three large categories: fat, stroma (connective tissue, mostly), and glandular tissue, called parenchyma, made up of ductal epithelial cells. On a mammogram, the light parts on the image represent the “gland” part. The dark parts are the fat. In humans, the gland is made up of numerous ducts snaking through the fat and stroma like tendrils of fireworks in the night sky.

If you want to learn how a car is made, you go to the assembly plant. If you want to know how breasts develop, you visit Zena Werb, a cell biologist in the anatomy department at the University of California, San Francisco.

The first thing she’ll tell you is that we don’t know much.

Oh, we know some things, like basic breast dimensions. The average breast weighs just over a pound, but this can double in late pregnancy. Its mean volume is about
²
/
₃
cup, or 561 milliliters. (The woman said to have the largest implants in the world, though, wore a size 38KKK, the fluid equivalent of 2.6 gallons, or 21 pounds. She reportedly contracted a staph infection in her breasts and had to get the implants removed. As one news outlet put it, “What goes up must go down.”) Over the course of a menstrual cycle, breast volume varies by 13.6 percent, owing to water retention and cell growth. Some studies have found that the left breast tends to be bigger than the right breast. In any case, one breast is usually, on average, 39.7 milliliters, or nearly a fifth of a cup, bigger than the other.

For decades, the standard way to measure volume was to make a plaster cast of each breast, then fill it with sand “of known density.” Bra manufacturers prefer to use standard mathematical for
mulas. They take into account radius and diameter and cone shape versus hemisphere shape. They look like this:

These equations are taken from a mechanical journal published in the wake of Sputnik. Its proud author declared, “Brassiere design is one engineering activity, at least, in which the United States is ahead of the Soviet Union.”

Werb is not interested in measurements. She is unlocking the mysteries of how breasts develop. While visiting her at her small office on a high floor of the UCSF Medical Center, I saw breasts everywhere. Werb wore a broche of gold concentric circles pinned to her black jacket. She had on gold hoop earrings and round glasses. A self-portrait of Frida Kahlo lactating hung on the wall in a frightful
Madonna lactans
twist that only Kahlo can do. Against another wall leaned a glow-in-the-dark skeleton. Life and death. Breasts confer both.

Unlike any other organ we have, breasts do most of their developing well after birth. In other complicated organs, such as the brain, the penis, and the testes, the basic architecture is laid down at birth. But the breast has to fully build itself out of nothing during puberty. Even then, it’s not done. The gland grows new milk-making structures under the influence of pregnancy hormones. Once an infant has weaned, a switch flips somewhere and the gland shuts down and shrinks. The breast must construct and then deconstruct itself over and over again with each pregnancy. It’s like Caesar’s army, making a camp city and then breaking it down on its relentless march across Gaul. Even if a woman never gets pregnant, her breasts pack and unpack a little bit each month just in case.

The developing breast is a challenging organ to study because, as Werb pointed out, you can’t easily find adolescent tissue samples to cut open. After a twelve-year-old girl has been killed in a car crash, you can’t just go up to the parents and say you want her breasts. “There’s a question of delicacy,” she said.

So for the most part, Werb does what many of her breastresearching colleagues do. She spends a lot of time with mice and rats. Among other things, she’s discovered how glandular tissue grows, literally, molecule by molecule. This fruiting out is called mammapoiesis, a word that makes me think of breasts reciting poetry, which seems somehow apt. Werb has actually caught it on video. It’s breast porn of a whole new kind.

She showed me the action footage of molecules becoming glands becoming breasts. Brilliant green dots appeared, forming a kind of shoreline. The dots, tiny rings at the front of a shoreline, slowly bubbled outward. They were the little milk ducts tunneling forth as they grow during puberty. It looked so innocent. But then she described the shoreline as “the invasive front.” I felt like I was watching a reenactment of D-day, and in a way, I was. Ductal cells grow into surrounding tissue by massively proliferating. If that sounds familiar, that’s because it’s essentially the same process that occurs in cancer, except here, it’s supposed to happen. At some mysterious signal in late childhood, the milk ducts set out on their journey, forming dense, veinous branches. The surrounding tissue, mostly the stroma, including material called the “extracellular matrix,” permit the trespassing ductal cells to cross.

Werb’s work illustrates how the different cells of the breast are constantly communicating; the extracellular matrix must allow the gland to grow through it, possibly because the glandular cells command it to. In cancer, a tumor sends out similar signals. If we
can learn more about the molecular stop and go signals of development, we’ll have more clues for treating cancer. Essentially, it looks as though cancer cells just think they are making another breast.

WERB’S IMAGES WERE TOO HIGH-TECH AND ABSTRACT FOR ME. I
needed to step back from the microscope to see the bigger picture. Thankfully, I had my handy copy of Sir Astley Cooper’s
On the Anatomy of the Breast,
originally published in 1840. Back when he was writing, it was easier to scrounge up dead people’s organs. As a result, some of the best work on breast anatomy is 170 years old. (This begs a digression. In England, the king granted surgeons free use of the organs and bodies of up to a hundred executed criminals a year. But soon that wasn’t enough—and it didn’t include many breasts in any case—so medical schools turned to the cadaver trade. It wasn’t technically illegal to take someone’s dead body, because corpses, unlike the clothes attached to the corpse, weren’t considered property. Grave robbers, so-called resurrectionists, became so prominent they actually organized unions and went on strike for better corpse prices. After a huge scandal involving a Scottish boardinghouse whose proprietor murdered drunken tenants for the body trade, Parliament passed the Anatomical Act of 1832. This required anyone performing dissections to have a license and to use only bodies that were donated or left unclaimed in prisons and workhouses.)

Born in 1768, Cooper was a gifted British physician. In 1820, he achieved fame (and a baronetcy) after removing an infected cyst from the head of King George IV. He became surgeon general to the king and later to Queen Victoria. In his sixties, Cooper turned his attention to “senology,” or the study of the breast, from
seno,
Italian and Spanish for “bosom” (not to be confused with Sinology, the
study of China). However he got them, Cooper harvested breasts from dead females (and quite a few males) of every age and inclination. It sounds morbid (okay, it
is
morbid), but Cooper found these dismembered breasts very beautiful. He became their most faithful and celebrated chronicler and would would lend his name to a set of bosomy ligaments.

It’s not surprising that doctors were fascinated by breasts. For one thing, they were a known source of tumors. But most incredibly, these organs performed the transmutation of blood to milk. Even Jesus Christ could work with only loaves and fishes. How did this alchemy work?

Cooper knew it worked slightly differently in different mammals. Cows have one major channel flowing out of the teat. It’s the Erie Canal, compared to the Nile Delta in humans, rivulets that emerge from the nipple through tiny holes like those at the tip of an old-fashioned watering can. To study the complex ductal system, Cooper injected more than two hundred (dismembered) breasts with wax dyes or mercury in a scientific quest one modern Scottish anatomist called “a breadth of experience unparalleled before or since.” Cooper then drew detailed “galactograms,” or images of the milk duct system, which he published in his definitive text. The renderings are available on the Internet (as are so many less scientific images of breasts), and they are fascinating. The ducts appear rubbery and stringy and convoluted—seaweed salad in a bowl. For his reader’s edification, Cooper also includes plates showing The Udder of the Ewe and the Dug of the Ass.

The descriptions of Cooper’s “preparation” read a bit like an old farmhouse cookbook: “it is requisite that the breast be put for a short time in boiling water, when the skin and fat become detached, and the gland, like other albuminous compositions, is left extremely
hardened … dried, after being boiled, the gland may be preserved for many years.”

Cooper labored under no delusions about who or what breasts were for: “in all the class Mammalia, [Nature] has provided glands to supply bountifully, by the secretion of milk, that nourishment which the young animal will require soon after it begins to breathe. The Breasts, or Mammae, are formed for this purpose.” This perspective does not, however, keep him from often referring to the breast’s elegance and pleasing appearance.

Through his meticulous dissections, Cooper learned more about the breast than just about anyone before or since. Among his many astute observations was that the blood-to-milk miracle happens in the alveoli cells deep in the gland, in tiny grapelike structures that form lobules. The lobules merge into separate ductal networks called lobes. If the lobules are the grapes, the lobes are the vines. These make up the breast’s basic dairy equipment. The number of lobes varies among women, with the average being two dozen. Each lobe empties out into an orifice on the nipple, and sometimes different lobes share one orifice. The average nipple has about twelve orifices. When the gland is developing in childhood and puberty, growth starts at the nipple and branches backward toward the chest wall, and during pregnancy the lobules with their alveoli finally form.

Cooper did not know about the breast making stem cells, but he discovered many other wonders, such as the ability of the nipple to secrete substances other than milk, including protective oils. He saw that the areola has little bumps to help form a seal with infant lips. He recognized the glands are densely wired with veins and nerves, all the better for responding to infants and stimulating lactation (this is also why the breast is so sexually responsive, but Cooper—ever the Victorian—didn’t write specifically of its erotic capacity). He exam
ined the properties of breast milk and even made cream cheese from it. He told his medical readers how to distinguish a benign from a malignant tumor, and how and when to operate.

Cooper noted that sometimes men grow breasts, and on rare occasion have been able to produce milk-like fluid. This happened to a twenty-two-year-old soldier he examined. When male or female breasts produce milk unrelated to pregnancy, the condition is called (rather uncharmingly) galactorrhea. He correctly observed that man-boobs are usually made of fat and not gland, but he saw that there are small amounts of glandular tissue behind the male nipple, including, sometimes, ducts. We now understand this to be the result of unusual hormonal influences such as a pituitary disorder or environmental exposures. Newborn babies also sometimes produce milk, called witch’s milk, the result of maternal hormones coursing through the baby.

Why do some men have breasts, and moreover—that perennial biology question—why do men have nipples? Cooper understood that both males and females are equipped with the same hardware early in fetal life, but he didn’t speculate on how they grew distinct. Here’s a newer bit of developmental biology: After an embryo is conceived, it is rigged to become either sex. This is called its bipotential state. During its first six weeks, certain pre-organ structures are laid down, including two parallel milk ridges. Born of ancient genes and common to all mammals, these ridges run up and down the length of the torso. If the fetus inherits female XX genes and the process unfolds in the expected way, then estrogen will turn the primitive plumbing into a female reproductive tract. If the fetus inherits male XY genes, testosterone will inhibit that progression. Since a later dose of estrogen can make male breasts grow, and then a hit of prolactin can fire up milk-making, it would theoretically be possible
to have fathers become full partners in lactation. They could take a milking pill. But good luck with that one.