But while the disease is rare, it is also ruthless. Worldwide, 87 percent of children stricken with retinoblastoma die. Survival is best in developed countries, but even among the children who have the disease in these nations, 97 percent suffer moderate to severe visual impairment as a result.
"Most of these cases involve the removal of one eye at least," Murphree noted. "Obviously, for young parents who face a diagnosis of a cancer in their child that is both life-threatening and vision-threatening is very difficult."
The other characteristic of the cancer that makes it so dangerous is the fact that it is very difficult to detect. Santos, like most other parents, had taken her baby girl to all of her recommended checkups, the most recent one at 9 months. While the cancer was most likely present in Rowan's eye at this time, even the pediatrician missed it.
Murphree said the test that would best reveal whether or not a child indeed had retinoblastoma would involve dilating the eye with eye drops -- a test that is not currently a standard practice among pediatricians. Years ago, Murphree spearheaded an effort to make these tests routine. But because the disease is so rare, most doctors remain opposed.
"The problem is that pediatricians will see one case of retinoblastoma in 30 years of practice," he said. "You would have to do [the test] in 15,000 healthy babies before you find it in one."
But as in the case of Rowan Santos, another means to detect signs of retinoblastoma and other eye problems in infants may be as close as the family camera.
"The 'red eye' look that the public dislikes is the tell-tale sign of a healthy eye," Taub said. "The lack of it is the clue there is something wrong."
In fact, Taub said she and her fellow ophthalmologists regularly ask families to bring in photos: "We call it F.A.T. -- family album tomography."
"The flash camera can be used usefully for home diagnosis of infant and child problems," said Seattle ophthalmologist Dr. Richard Bensinger.
"If in a series of photos, the same eye always is red and the other dark for your child, then the dark eye may be always turned away from the central axis and might be crossed," Bensinger said. "This could be due to ordinary misalignment, which can be fixed, or due to something inside the eye blocking normal vision, such as a tumor, or cataract, or other internal obstruction, which needs attention right away."
Vigilance is especially important for parents with a family history of the disease.
"Those with a family history should be very alert," said Dr. Harry Quigley, director of the Dana Center for Preventive Ophthalmology at the Johns Hopkins University's Wilmer Institute in Baltimore. "An eye deviating to the side compared to the other eye after age 3 to 4 months should be examined by an ophthalmologist."
Quigley added that infants who rub their eyes regularly or who have severe redness in their eyes should also be checked out.
But for Santos, one of the most important steps turned out to be sharing her concerns in a supportive online community. Phone messages left with Robb were not immediately returned. But Santos said that the U.K. mother continues to offer support as Rowan, who turned 1 on Aug. 20, faces the months of treatment ahead.
"I love her," Santos said of Robb. "She was very brave to send the e-mail she did because cancer is a very scary thing to have to tell someone about."
"She is an amazing woman. I will always be grateful to her, and my family will always be grateful."
ABC News information specialist Brad Martin contributed to this report.