It makes many good points, one of which is the siliness of viewing cancer in general, or of any particular organ, as being a single entity. Genitourinary and GYN malignancies are sill fresh in my mind after this last rotation, so an example that comes first is prostate cancer. Most have your standard testosterone-dependent, androgen deprivation therapy-sensitive cells. Once they stop responding to hormonal therapy, treatment is still targeted towards the (now mutated) androgen receptor. Small cell prostate cancer, however, looks and behaves differently—tending to be bulkier, more aggressive, and having earlier visceral organ metastases. Ultimately, we treat it more like its namesake in the lung, with cisplatin and etoposide.
That was an easy distinction to make, since small cell prostate cancer looks nothing like adenocarcinoma under a microscope. Not so for breast cancer. We now know that it is at least four diseases which are at first glance all the same: luminal A (hormone receptor-positive, Her2-negaitve); luminal B (HR-positive, Her2-positive); HR-negative, Her2-positive; and triple-negative (also called basal-like, though definitions of basal-like breast cancer vary). The first three, which we are now able to distinguish with immunohistochemistry and FISH, have different behaviour, treatment, and prognosis. The fourth is a catch-all category that probably contains many different diseases we don't know about yet. Some of those triple-negatives may have more in common with colon or lung cancer than they do with other malignancies of the breast.
Which organ the cancer is in should be important to a surgeon or a radiation oncologist, who have to deal with the anatomy. But should medical oncologists subspecialize by organ, or by cell? Why is a neuro-oncologist better suited to treat primary CNS lymphoma than a hematologist whose main interest are aggresive lymphomas? Does a GI oncologist have a better skillset and knowledge base for dealing with neuroendocrine tumors of the pancreas than an oncologist who deals with endocrine gland malignancies? Are there other, not so obvious connections between different cancers that we are missing because of ultrasubspecialization?
I don't know enough oncology to answer any of these questions, but they are interesting questions to make.