In 2012, my mother was diagnosed with pancreatic cancer, a type that’s most often caught late and has a poor prognosis even when caught early. My mother was diagnosed at Stage III, when her tumor had already grown into the wall of an artery, making surgical removal impossible. She decided to undergo chemotherapy anyway, not because it would save her life—not even because it would extend her life, though it undoubtedly did, by weeks or even months—but because it might lessen the pain she was likely to experience as the growing tumor began to press on her organs, blood vessels, and nerves. Despite the difficult side effects of chemo, my mother’s treatment was palliative, designed to make her as comfortable as possible for as long as possible.

At first, she received the chemotherapy drugs via a peripherally inserted central catheter, or PICC line, a tube that’s inserted in a vein in the arm and threaded up toward the heart. It was a cumbersome contraption bandaged to my mother’s inner arm, interfering with her sleeves and her movement. Because the tubes extended outside her body, the PICC could easily be damaged or broken, and would often clog up unexpectedly. It also increased her risk of developing an infection; at one point, she had three of them at the same time.

When it became clear than the PICC wasn’t working—besides the infections, she also suffered from blown veins in her arms—doctors placed my mother under anesthesia and implanted a medical port the size of a quarter under the skin near her collarbone.

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According to the Centers for Disease Control, my mother was one of approximately 650,000 people who undergo chemotherapy treatment annually in the United States. The medical port has become an integral part of treatment for many of them.

Because many chemotherapy drugs are so toxic that they easily damage smaller blood vessels and surrounding tissue, they can’t be repeatedly administered via the more commonplace IV infusion into veins in the hand or arm. Ideally, chemotherapy drugs would directly enter the vena cava, a large vein leading into the heart’s upper-right atrium that’s less easily damaged. With no valve between the vena cava and the heart’s chamber, it’s also as close as something can be placed to the heart. When the drugs enter there, they are drawn quickly into the heart and propelled efficiently throughout the body—less damage, faster circulation.

Earlier devices like the PICC and the Hickman, which dangles out of the body through a hole in the chest, deliver their drugs this way, and they perform relatively well for the job of administering chemotherapy. But because some parts remain outside the skin, these gadgets—besides being invitations for infection—can make everyday actions more difficult or uncomfortable. In some patients, for example, a Hickman lies in the same spot where a seatbelt would hit. Both PICC and Hickman lines also require daily flushing to keep the tubes clear—a constant reminder of illness, as well as an annoyance. What cancer care needed was some kind of transfer device for which all the parts could be placed entirely inside the body—and the medical port, which achieves these two goals, caught on quickly after its introduction in the 1980s.

The word port evokes the image of ships sailing in with goods. It’s a place where cargo is transferred from sea to land or, in reverse, sent off from one place to another. Similarly, a medical port is such a way into the body, a point of access where powerful drugs can be transferred from the world outside the body into the liquid that circulates through it. Because blood can be drawn via the port, it is also a point through which things can leave.

The flat side of the port that lies just beneath the skin near the collarbone is a self-sealing sheath of silicone. This sheath, or septum, can withstand hundreds of needle jabs, perhaps as many as 2,000, without leaking or breaking down. Beneath the septum is a small reservoir, and out of the back of this reservoir runs the catheter into that large vein above the heart. Some reservoirs are made of titanium, while others are stainless steel, plastic, or some combination of materials. Ports and the attached catheters can also vary in shape and size. Because the port serves one function, however, the basic design remains the same, no matter the type: sheath, portal, catheter. After implantation, the port becomes part of the body. It sits under the skin, nearly attached to the heart, intimately part of the cancer patient.

Medical objects inside the body have become more and more common. We are organic life forms, but many of us have mechanical parts. My sister has a metal plate and screws in her back. My father-in-law had his knee replaced. My aunt had a pacemaker. Some people have arterial stents to improve blood flow; others have cochlear implants to improve hearing. When an object is inserted inside a person, it becomes a part of that person—the body puts it to use immediately and depends on it to function optimally.

The medical port is subtly different—it’s both of the body and not of the body. The port is an object of convenience for the patient and the cancer-care providers, but the body itself doesn’t find the device particularly useful, nor does it become dependent on the port for any particular function. When it’s no longer needed, it’s removed through a simple surgical procedure. In this way, the port remains its own separate entity, even as it sits entirely inside the person’s physical form.

My friend Patricia Grace King, a fiction writer, had a port during her chemotherapy treatment before surgery for breast cancer. She wrote of her experience on her blog:

I have been so hyper-fixated on my left breast and the lump in it, but now I’m aware too of my new port, just over my right boob and it feels like a good counterbalance. The port is there now on the right boob to fight and kill the cancer in the left boob. Every time I feel it—the port—I think of that, and it’s good.

The port made Patricia feel strong, in other words, because it symbolized the action she was taking to destroy the tumor inside her. It was part of her body, at least temporarily—and part of her mindset, too, a strangely welcome addition to herself while she needed it.

Most of the time, my mother thought nothing of her port. For a cancer patient, especially for someone with a poor prognosis, the port is often low on the list of concerns. (When it was time to be stuck with a needle, though, she was both aware of the port and grateful for the way it guaranteed that she would only need a single prick—a blessing for cancer patients and medical staff alike, as drawing blood from the small, compromised veins of a chemotherapy patient can be a difficult and painful process.) But as my mother lost weight, the port became a more prominent lump, one of many reminders of her illness—a symbol of her status as a cancer patient, separating her in a small but significant way from the person she had been a few months earlier. Occasionally, she would run her fingers absentmindedly over the port, lightly brushing the bump of skin, as if to remind herself it was there.