There is little to add to the cogent points made in the previous post, but perhaps, the reader might wish to also consider this:
The doctor who gives the speaker the prognosis that his time on earth is short is the first person to "give[n] me/something no one else on earth had ever given me," and, as such, he awakens in the speaker a new zest for life. For, it seems that after the speaker is told that he may not live long, he wants to live more than ever; he now appreciates life now because of the reality of it being taken from him. In the words of an old popular song, "You don't know what you've got, until you lose it." So, a theme of this poem can be the irony of how much more appreciative people are of that which is threatened with loss.
There can be several themes in Carver's poem. I think that two of the most interesting involve human relationships and the exploration of death. The way in which relationships form is a significant theme in the poem. The poem offers an examination of the relationship that exists between human beings. Carver's poem brings out how there are ties that bind all human beings. The relationship shared between the doctor and the patient in this poem is essential. It is one where realities such as life and death are understood. The relationship is difficult for the doctor to appropriate. Being a man of science and not being able to fully empathize with the condition of death is distinctive. The doctor is able to articulate the conditions that cause death, but is unable to communicate anything meaningful about it:
he said I’m real sorry he said
I wish I had some other kind of news to give you
I said Amen and he said something else
I didn’t catch and not knowing what else to do
and not wanting him to have to repeat it
and me to have to fully digest it
The "some other kind of news" follows the Doctor having "stopped counting" the number of negative growths on an X- Ray of the patient. The relationship between both the doctor and the patient is bound by the condition of life and death. The patient adds the empathetic note to this relationship in how he "saves" the doctor from the awkward nature to repeat what he has already stated. The empathy in their relationship is evident in the patient's reaction: "I jumped up and shook hands with this man who’d just given me/ something no one else on earth had ever given me/ I may have even thanked him habit being so strong." The patient possesses a type of strength in their relationship that the Doctor lacked. While the poem began with the Doctor possessing power, it is the patient who ends up holding it. The relationship that exists between both becomes vitally important in the narrative of the poem. Carver's poem speaks to how relationships develop amongst people in the most unlikely of conditions.
Within the complexity of human emotions is also the intricacy of death. This is another major theme in the poem. Carver depicts a vision of death that is far from the traditional understanding of death. Death is not seen as something of an end. Rather, it is viewed in a context of liberation. The doctor has given the patient "something that no one else on earth had ever given." The liberation quality of death also helps to define how the patient responds to the Doctor's news. The ending is different than the start, both in the poem and in the understanding of death. The opening of the poem is predicated upon something that "is not good." Yet, the ending of the poem is one in which death has triggered the empathy in the patient that he assists the Doctor. At the same time, death is something that lies outside of the calculations and statistical analysis of medicine. It might be for this reason that the Doctor is speechless and the patient is able to communicate far more. The complexity of death is a theme that is explored in the poem. Its wide ranging implications upon human behavior and relationships is significant in the thematic understanding of the poem.