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.