Which of the following is NOT an early response to radiation exposure?

Breast cancer is classified as a late effect of radiation exposure rather than an early response. Early responses typically manifest soon after exposure and reflect immediate biological changes to cells and tissues. Chromosome aberrations, for instance, can occur almost immediately following exposure, as they reflect the direct damage to the DNA within cells. Intestinal distress occurring about a week after exposure falls into the category of acute radiation syndrome, also indicating an early response. Epilation, or hair loss, can also occur soon after exposure due to damage to the hair follicles.

In contrast, the development of breast cancer is a complex process that can take years or even decades to manifest. It arises from cumulative effects of radiation and other risk factors and does not present as an immediate reaction to radiation exposure, making breast cancer the correct choice for the answer to this question.