Pregnant woman (Ivory Coast)
Pregnant woman (Ivory Coast, West Africa)

Recently I’ve mentioned a few cases of transmissible tumors — that is, cases where tumors actually spread from their original host, to other individuals. The two most dramatic transmissible tumors are Canine Transmissible Venereal Tumor (CTVT) and Tasmanian Devil Facial Tumor (TDFT), where the original tumor can spread widely throughout the entire species. (See this post, this one, and this one, for more detail.) There’s also at least one case of a tumor that accomplished a single transmission, from the original patient to the surgeon who operated on him. 1

Tumors aren’t supposed to be able to spread in this way, because they’re essentially foreign transplants — they should be rapidly rejected, as if they were, say, a skin graft between two random people. In this post I talked about how CVTV and TDFT might have arisen. (There are also a number of cases of tumors that spread to immuno-suppressed individuals, such as after organ transplants, but those cases are easier to understand from an immunologic viewpoint.)

When checking up on references for the last post, I ran across a set of transmissible tumors I hadn’t known about: Vertically transmitted tumors, in which tumors spread from a pregnant mother to the fetus in utero.2

This also, I’m glad to say, seems to be very rare, as you’d expect. Even though mother and child are partially tissue-matched, and even though pregnancy is a very special situation, immunologically, the parent and her child are not genetically identical, and should reject grafts from each other pretty efficiently. (Transplants from parent to child still require immune suppressive treatment.) The review I ran across lists a total of 14 cases of vertical spread of tumors, from 18663 to 2002.4 Although they do note that:

Given the lag time between birth and diagnosis in several of the infants, cases of maternal–fetal transmission may not be as rare as the literature would suggest, and the number of cases could be higher as the detection of metastatic tumor in the fetus may go undetected in cases of abortion or maternal–fetal demise. 2

Malignancy during pregnancy isn’t all that uncommon (0.1% of pregnancies, it says here), so the handful of cases with actual spread of the tumor to the fetus are “numerically inconsequential”. What was different about these 14 cases? We don’t really know, in general. Almost all of the described cases are earlier than 1965,5 predating the molecular era of medicine. Perhaps some, or many, of the infants were immune compromised, as the authors note:

Fetuses with a congenital immunodeficiency are likely to be at an even higher risk for the engraftment of such tumor cells.6 Other factors that may affect the likelihood of tumor cells entering the fetal circulation include maternal homozygosity for one of the fetal HLA haplotypes,7 metastatic potential of the maternal tumor, and a high maternal blood and/or placental tumor load. 2

The outcome of this transmission was very poor; only 3 of the 14 children survived the disease.

I don’t really have any lesson to draw from these cases. Without an extensive molecular workup that isn’t available for almost all of these cases, I don’t know that we can learn much about tumor transmission. Still, these stories are worth keeping in mind when thinking about mechanisms of tumor transmission.

  1. Gartner HV, Seidl Ch, Luckenbach C, et al. Genetic analysis of a sarcoma accidentally transplanted from patient to a surgeon. N Engl J Med 1996;335:1494–1496.[]
  2. Tolar J, & Neglia JP (2003). Transplacental and other routes of cancer transmission between individuals. Journal of pediatric hematology/oncology : official journal of the American Society of Pediatric Hematology/Oncology, 25 (6), 430-4 PMID: 12794519[][][]
  3. Friedreich N. Beitrage zur pathologie des Krebses. Virchows Arch 1866; 36:465–477.[]
  4. Tolar J, Coad JE, Neglia JP. Transplacental transfer of small cell carcinoma of the lung. N Engl J Med 2002; 346:1501–1502.[]
  5. Not saying the molecular medicine abruptly switched on in 1965, it’s just a convenient cutoff[]
  6. Pollack MS, Kirkpatrick D, Kapoor N, et al. Identification by HLA typing of intrauterine-derived maternal T cells in four patients with severe combined immunodeficiency. N Engl J Med 1982; 307:662–666.[]
  7. Osada S, Horibe K, Oiwa K, et al. A case of infantile acute monocytic leukemia caused by vertical transmission of the mother’s leukemic cells. Cancer 1990; 65:1146–1149.[]