One of the men I was exchanging emails with last year told me that his doctor told him that if he drank a lot of milk growing up, it wasn't matter of if he would get prostate cancer but when. I thought that was remarkable at the time, because rarely do mainstream doctors get excited about anything nutritional. Since then, I have kept my eyes out for anything related to the subject and was shocked to find out just how many possible milk-related links there were to cancer. And, by the way, this is not something that I wanted to hear. I love nonfat yogurt and didn't want to give that up and non-fat dairy is part of some low fat diets. But the evidence below is just too overwhelming in my opinion, especially if you're 55 like me.
Here are Four Significant Links of Milk and Dairy to Cancer or Cancer Formation:
1. Not For Adults. I don't need to tell anyone that anything that comes out of a mammary gland is NOT designed for adults. Milk is for infants and it is designed to be highly stimulatory and make sure the baby (cow, human or whatever) grows fast and grows strong. Yes, mammary milk is designed to drive growth - growth at all costs - and infants can grow tissues like weeds, because they are almost entirely impervious to cancer. That is not true with an adult. See #2 below:
2. Growth Factors (VEGF and EGF). Some of you may have heard of the Anti-Angiogenic Diet. There is a well-known Ted Talk on the subject by Dr. William Li.  Basically, Dr. Li talks about eating a variety of plant foods that inhibit growth factors that feed the growth and spread of cancerous tumors. The most infamous of these growth factors are Epidermal Growth Factor (EGF) and Vascular Endothelial Growth Factor (VEGF).
We all need some EGF and VEGF, of course, for tissue repair and wound healing. Furthermore, there is (an animal) study that shows, for example, that diabetics can become deficient in these growth factors. However, generally speaking, you don't want to deliberately stimulate VEGF and EGF - that's asking for trouble - and is source of considerable research. Look what this research summary says:
"Angiogenesis is essential for cancer development and growth: before a tumor can grow beyond 1 2 mm, it requires blood vessels for nutrients and oxygen. The production of VEGF and other growth factors by the tumor results in the angiogenic switch , where new vasculature is formed in and around the tumor, allowing it to grow exponentially. Tumor vasculature formed under the influence of VEGF is structurally and functionally abnormal. Blood vessels are irregularly shaped, tortuous, have dead ends and are not organized into venules, arterioles and capillaries. They are also leaky and hemorrhagic, which leads to high interstitial pressure. These characteristics mean that tumor blood flow is suboptimal, resulting in hypoxia and further VEGF production. This central role of VEGF in the production of tumor vasculature makes it a rational target for anticancer therapy." 
Now what is the one thing that most people over 40 should probably NOT do? You guessed it - we would not want to drink something that actually contained significant VEGF and EGF, right? Well, milk contains both of these growth factors and in significant quantities. Why? Because milk is designed for calves. Mother Nature wants that calf to put on a couple of hundred pounds in just a few months and those growth factors are her magic recipe.
As you might imagine, the Paleo leaders are jumping all over this, since a classic Paleo Diet is not supposed to contain dairy. Loren Cordain, the founder and chief apostle of the modern Paleo movement, recently showed that, not only does milk have EGF, but it has a beefy - no pun intended - quantity of it. Look at this quote from him regarding the amount of betacellulin, a form of EGF, in milk: 
"So what what if a little betacellulin from cow s milk gets into your bloodstream does it matter? You bet it matters. A liter of whole milk (633 kcal) contains 1,930 nano-grams of betacellulin whereas the amount of EGF that your salivary glands secrete is only 35.3 ng per day. The binding affinity of betacellulin to the EGF receptor is greater than that for EGF; consequently betacellulin can displace EGF from the EGF receptor. The amount of betacellulin that you get from drinking even a single cup of milk (457 nanograms) has the capacity to stimulate the EGF receptor 10 times more than what normally would occur during a 24 hour period from EGF in saliva."
Remember that research shows that about half of men over 40 have small cancer nodules in their prostate. Everything is fine as long as these nodules stay small. But throwing a boatload of growth factors into your bloodstream and just begging that nodule to turn into a full-fledged tumor is just not a good idea.
2. Casein and Dr. Campbell. Many of you may have heard of Dr. Colin Campbell and The China Study. His book has been very controversial, but I want you to forget about all of that for a second. Dr. Campbell actually did an impressive set of animal studies well before The China Study. His early work showed that casein, the cheif milk protein, could induce liver cancer in animals. He did a number of studies that showed that, if you went above a certain percentage of casein in the diet, that the risk of liver tumors greatly increased.
Since Dr. Campbell is so controversial with American meat eaters, I want to jump past his research and fast forward to more recent scientific history. Evidence had been assumulating that casein, specifically the A1 beta-casein in milk and diary, is pro-inflammatory. And, in fact, a 2014 study found that it was not just a little inflammatory, but rather highly inflammatory. They found HUGE increases in IL-4 and summarized their findings by saying that "It is reasonable to conclude that consumption of A1 "like" variants of -casein induced inflammatory response in gut by activating Th2 pathway as compared to A2A2 variants. The present study thus supports the purported deleterious impacts of consumption of A1 "like" variants of -casein and suggests possible aggravation of inflammatory response for etiology of various health disorders." 
That's an incredible assertion if you stop to think about it: these researchers were willing to go on record saying that milk could cause other medical conditions. Keep in mind that this was not in a backwater journal, but rather the European Journal of Nutrition.
Because many health leaders are finally - hallelujah! - emphasizing the importance of gut health and flora, this will likely rise to prominence. Notice that A1 beta-casein appears to literally inflame the gut and thus could cause a host of issues. One thing to warn friends and family about: the primary issue with A1 beta-casein is that it causes gut bacteria to release a molecule name BCM-7. There is accumulating evidence that BCM-7 is the driver of autism, SIDS (Sudden Infant Death Syndrome) and other childhood disorders.
Now let's jump back to Dr. Campbell's research. What does inflammation have to do with cancer? Everything! Cancer has been linked to inflammation time and time again and inflammation is considered one of the leading causes of inflammation, along with elevated growth factor levels and DNA damage. Clearly, Dr. Campbell's earlier work makes a lot of sense in retrospect.
A HACK? As an fyi, there are a couple of companies that have developed A2 beta casein milk, which appears to be much more benign. I don't know where or if you can purchase it.
3. High Calcium. Guys who love milk usually drink a lot of it. I used to have a huge bowl of cereal in the morning and in the evening through most of my early adulthood - just loved the stuff. Guys who do this end up consuming unnatural levels of calcium and this has been linked to prostate cancer due to the fact it supresses the body's production of calcitrol, which is involved in the body's fight against cancer. 
4. Elevated IGF-1. Milk also stimulates IGF-1, another growth factor that many bodybuilders and strength athletes are familiar with. IGF-1 can help build muscle, repair tissue, etc. However, it has, like EGF and VEGF, been linked to many types of cancer. Furthermore, lower levels of IGF-1 is now being extensively studied in anti-aging research, because doing so appears to extend lifespan and powerfully protect against diabetes and cancer. Look at what this paper said about casein, the primary milk protein:
"The main milk protein fractions exhibit important but different growth-promoting effects by increasing either fasting insulin (whey) or IGF-1 (casein) levels." 
By the way, milk defenders will often raise up a straw man claiming that the IGF-1 in milk gets denatured in the digestive tract and does not make its way into the plasma. That is irrelevant, however, because casein stimulates our own IGF-1 production.
SO IS THERE EPIDEMIOLOGICAL DATA LINKING MILK and DAIRY TO CANCER? Let's look at a couple of examples:
"However, a strong positive association with milk consumption was observed for cancers of the lymphatic organs (odds ratio 3.4 for greater than or equal to 2 glasses per day vs less than 1; 95% confidence interval 1.4-8.2). An inverse association was found for cancer of the bladder. Kidney cancer and cancers of the female reproductive organs (except the uterine cervix) showed weak positive associations with milk intake." 
"Our results support the hypothesis that high calcium intake may increase risk of prostate cancer, and this relation may underlie previously observed associations between dairy products and prostate cancer." 
"These results support the hypothesis that dairy products and calcium are associated with a greater risk of prostate cancer." 
REBUTTAL? Interestingly enough, there was a large pooled study that found that low fat dairy actually lowered colon cancer risk. Also, a couple of prominent studies found that non-fat dairy was protective and regular fat dairy promoted cancer. My personal take on this is that this is probably because low fat dairy can help with Met-S (Metabolic Syndrome or prediabetes). It is possible that the beneficial effect of improving Met-S may in some populations improve cancer outcomes. However, in healthier populations, I simply cannot foresee how lowering calcitrol, boosting IGF-1, inflammation, VEGF and EGF is going to possibly help with cancer, especially in the 40+ crowd.
1) https://www.ted.com/talks/william_li?language=en, "Can We Eat to Starve Cancer?"
2) The Egyptian Journal of Histology, Jun 2011, 34(2):403-414, "Effect of sildenafil (Viagra) on epidermal growth factor expression in submandibular gland of diabetic male rats: histological and immunohistochemical study"
3) Oncology, 2005, 69:4 10, "VEGF as a Key Mediator of Angiogenesis in Cancer"
5) Eur J Nutr, 2014 Jun, 53(4):1039-49,, "Comparative evaluation of cow -casein variants (A1/A2) consumption on Th2-mediated inflammatory response in mouse gut"
6) Cancer Epidemiol Biomarkers Prev,2006,15(2):203-10
7) Eur J Clin Nutr, 2009 Sep, 63(9):1076-83, "Differential effects of casein versus whey on fasting plasma levels of insulin, IGF-1 and IGF-1/IGFBP-3: results from a randomized 7-day supplementation study in prepubertal boys"
8) Br J Cancer, 1990 Mar, 61(3):456 459, "Milk consumption and cancer incidence: a Norwegian prospective study"
9) Cancer Causes & Control, December 1998, 9(6):559-566, "Dairy products, calcium, phosphorous, vitamin D, and risk of prostate cancer (Sweden)"
10) Am J Clin Nutr, October 2001, 74(4):549-554, "Dairy products, calcium, and prostate cancer risk in the Physicians' Health Study"