WebMD: “While the number of men diagnosed with prostate cancer remains high, so does the number of men who get it and live. Survival rates after diagnosis of common types of prostate cancer are:
5 years: nearly 100% survival
10 years: 99% survival
15+ years: 94% survival
“Prostate cancer is a slow-growing disease. You’re far more likely to die from other causes before you die from prostate cancer. You’re also more likely to catch it earlier if you get annual screening tests.” 
WebMD: “Prostate cancer treatments are improving, and men are being diagnosed earlier than in previous years. Men diagnosed with prostate cancer today might have even better survival rates than these. For example, the five-year relative survival rate for men diagnosed with prostate cancer in 1990 was 92.9%, and now it’s 99%.” 
The above statistics are for all men diagnosed with prostate cancer, regardless of the stage of the cancer. Taking into account the stage, the American Cancer Society says:
“Local stage means that there is no sign that the cancer has spread outside of the prostate. This corresponds to AJCC stages I and II. About 4 out of 5 prostate cancers are found in this early stage. The relative 5-year survival rate for local stage prostate cancer is nearly 100%.
“Regional stage means the cancer has spread from the prostate to nearby areas. This includes stage III cancers and the stage IV cancers that haven’t spread to distant parts of the body, such as T4 tumors and cancers that have spread to nearby lymph nodes (N1). The relative 5-year survival rate for regional stage prostate cancer is nearly 100%.
“Distant stage includes the rest of the stage IV cancers — cancers that have spread to distant lymph nodes, bones, or other organs (M1). The relative 5-year survival rate for distant stage prostate cancer is about 28%.
“Remember, these survival rates are only estimates — they can’t predict what will happen to any one man.” 
Diet Can Help
Many studies show that diet can influence one’s risk of getting cancer in the first place. And some recent studies also show that diet can affect the outcome after a diagnosis of cancer, decreasing risk of death or at least risk that the cancer will progress.
Here is a link to a review of recent studies on this topic:
Prostate cancer progression and mortality: a review of diet and lifestyle factors . The article includes many different considerations that affect risk of prostate cancer and its progression after diagnosis.
Below is a summary of dietary factors that influence the outcome after a diagnosis of prostate cancer, followed by a reference to the study indicating the risk or benefit.
30 mg/day (brand: Lyc-O-Mato)
In this study, men who took the lycopene supplement had smaller tumors, and the cancer was less likely to spread to the surrounding tissues, compared with men who did not take the supplement. 
Green Tea Pill
This study looked at men with “high-grade prostate intraepithelial neoplasia”, which is precancerous changes to cells in the prostate. The study authors state that 30% of men with that condition develop prostate cancer within 1 year. 
The study divided men with that condition into two groups. One group received a placebo, the other received a green tea extract pill containing green tea catechins (GTC). After one year, only 3% of the group treated with GTC developed prostate cancer, compared to 30% of the group that received a placebo. 
In addition, the study found that men with BPH (enlarge prostate) had a decrease in urinary symptoms after taking the GTC supplement. 
Could you obtain the same benefit from drinking decaffeinated green tea? The study only looked at the supplement. And the amount of green tea catechins found in actual tea varies a great deal.
Since tea contains some caffeine, choose a great tea extract pill that is decaffeinated.
Do NOT take Selenium Pills
A study of men with a diagnosis of prostate cancer found that “men who reported consuming 140+ mcg/day of selenium after diagnosis had a 2.6-fold increased risk of prostate cancer mortality.”  In other words, taking a selenium supplement (with 140 or more micrograms of selenium per day) more than doubled the risk of dying from prostate cancer.
A low dose selenium supplement did not show the same risk. But there is no compelling reason to take selenium, if you have prostate cancer. A low dose might still increase your risk to some extent. The study found an increase at low doses, but it did not reach statistical significance until 140 mcg or more per day. 
If you take a multivitamin, choose one without selenium.
Also, since Brazil nuts are very high in selenium, do NOT eat any Brazil nuts. Other nuts and seeds are a healthy choice.
Zinc from Food
This study found that men with a diagnosis of localized prostate cancer, were 76% less likely to die from that cancer, if they had a high intake of zinc from food. 
The study did not consider zinc as a supplement. The amount of zinc from food, need to obtain the above benefit was 15 to 20 mg per day. The best foods to eat for zinc are: wheat germ, pumpkin seeds, sunflower seeds, peanuts, tree nuts (cashews, pecans, etc.) and whole grain foods. 
A recent study of men diagnosed with prostate cancer found that drinking 4 or more cups of coffee per day reduced risk of prostate cancer recurrence/progression by 59% as compared to men who drank 1 cup or less per day. Results were statistically significant. This benefit was obtained regardless of whether the coffee was caffeinated or decaffeinated. No similar benefit occurred from drinking tea in this study. 
This study found that the prostate cancer cell proliferation rate — the speed at which the cancer cells multiplied — was significantly lower for men taking 30 grams (1 oz) per day of ground flaxseed. This health supplement is found in health food stores and many grocery stores. 
For men with prostate cancer, this study found a decrease in risk that the cancer would worsen, when the men ate fish two or more times per week. The fish may be baked or broiled, but not fried. Many studies showing a health benefit for fish did not find any benefit for eating fried fish. 
The same study mentioned above (fish), found a benefit when men with prostate cancer ate foods with cooked tomato sauce (also called pasta sauce or spaghetti sauce) two or more times per week. The study authors said that “diet after diagnosis may influence the clinical course of prostate cancer, and fish and tomato sauce may offer some protection against disease progression.” In other words, men who ate these foods more frequently, had a decreased risk that their prostate cancer would worsen. 
Although the study did not consider other cooked tomato foods, tomato soup would be likely to offer the same benefit as tomato sauce. The main tomato ingredient in both is tomato paste.
One study found that eating plenty of cruciferous vegetables, after a diagnosis of prostate cancer, reduced risk that the disease would progress by 59%. The authors wrote: “In conclusion, cruciferous vegetable intake after diagnosis may reduce risk of prostate cancer progression.” 
Cruciferous vegetables include: broccoli, cabbage, cauliflower, Brussels sprouts, kale, mustard, and chard greens. Many studies have found this type of vegetable to have beneficial effects on health, especially broccoli. In addition, cooking cruciferous vegetables has been found to deactivate some of the healthy compounds thought to be responsible for health benefits (indoles and isothiocyanates). So, of all the cruciferous vegetables, raw broccoli is perhaps best.
Maintain Stable Weight
This next point is surprising. A 2014 study found that either weight gain OR weight loss, after diagnosis of prostate cancer, increased risk of death. 
“A weight loss >5% after diagnosis almost doubled the rate of overall mortality compared to maintaining a stable weight … while a weight gain >5% was associated with an almost doubled increased rate of prostate cancer-specific mortality.” In other words, men who lost weight after diagnosis increased their overall risk of dying, but men who gained weight increased their risk specifically of dying from prostate cancer. Bottom line: maintain your weight while eating a healthy diet. 
Exercise by Brisk Walking
This study considered whether exercise, after diagnosis of prostate cancer, affected the progression of the disease (whether or not it got worse). “Men who walked briskly for 3 h/wk or more had a 57% lower rate of progression than men who walked at an easy pace for less than 3 h/wk….” This means that men who walk at a quick pace for 30 minutes per day, 6 days per week (3 hours total per week) were much less likely to have a worsening of their prostate cancer. 
The study also found that walking at a brisk pace decreased the risk that the disease would worsen, by 48%, regardless of the duration of the walking. So three hours of walking per week was better, but even a lesser amount of walking was very helpful, as long as the pace was quick. 
In another study, men who were more physically active, after a diagnosis of prostate cancer, had a lower risk of all-cause mortality and a lower risk of prostate cancer specific mortality than men who were less active. 
“Those who walked ≥ 90 minutes per week at a normal to very brisk pace had a 46% lower risk of all-cause mortality … compared with shorter durations at an easy walking pace. Men with ≥ 3 hours per week of vigorous activity had a 49% lower risk of all-cause mortality…. Men with ≥ 3 hours per week of vigorous activity had a 61% lower risk of PCa [prostate cancer] death … compared with men with less than 1 hour per week of vigorous activity.” 
Avoid Whole Milk
One study of men with prostate cancer found that drinking whole milk (one cup or more per day) more than doubled the “risk of progression to fatal disease after diagnosis,” as compared to drinking little or no whole milk. However, intake of other dairy products did not show any similar risk in this study. 
A similar study found that “Men with the highest versus lowest intake of whole milk were at an increased risk of progression,” (i.e. worsening) of their prostate cancer. However, the total intake of all kinds of milk and dairy foods “after diagnosis were not associated with a greater risk of lethal prostate cancer.” 
Avoid Poultry with Skin
One study found that “Greater consumption of eggs and poultry with skin was associated with 2-fold increases in risk….” The men with the least risk ate less than one half egg per week (on average) and avoided eating the skin of poultry. Chicken and other poultry meat did not increase risk when eaten without the skin. Each factor, eggs and poultry with skin, increased risk individually. 
Avoid Processed Red Meat
Processed red meat includes: sausage, pepperoni, bacon, hot dogs, salami, bologna, and other cold cuts. It does not include hamburger, steak, pork chops, beef stew, and similar foods.
Does eating processed red meat increase risk of advanced or fatal prostate cancer? Studies have shown mixed results. One study found an increase in risk of prostate cancer progression of 45%, but with borderline statistical significance. Another study found no statistical significance. 
However, there is ample evidence that eating processed red meat increases the risk of cancer, heart disease, other diseases, and overall risk of death. So a decision to avoid eating processed red meat is a healthy choice, but it may or may not help with the prostate cancer.
Decrease Saturated Fat
This study found that, among men with prostate cancer, “those with the highest omega-3 docosahexaenoic acid [DHA] and total marine fatty acid intakes were 40% less likely to die from prostate cancer.”  Results were statistically significant. DHA is found in fatty fish, such as salmon. It is also available in supplements.
The study also found that, specifically for “men with localized prostate cancer,” a high-fat diet (especially with saturated fats as found in butter, coconut oil, palm oil, and the fats of meat, poultry, and dairy) increased risk of “disease-specific mortality,” i.e. dying of prostate cancer. 
The take-away here is that you should eat fatty fish, decrease total dietary fat, and decrease all animal fats, especially butter.
Another study found that, among men with prostate cancer, those who ate the highest amount of saturated fat “had three times the risk of dying from prostate cancer,” compared to men who at the least amount of saturated fat. The study authors recommended reducing saturated fat intake “below 10% of energy” in order to “reduce the risk of dying from prostate cancer.” 
A third study found that “Replacing 10% of energy intake from carbohydrate with vegetable fat was associated with a lower risk of lethal prostate cancer … and all-cause mortality.” Men who ate less carbs and more vegetable fat had a lower risk of dying of prostate cancer and a lower overall risk of dying. But remember that a high-fat diet also increase risk, so the replacement of carbs with fat is limited (10% of daily calories). 
The same study found that higher intakes of saturated fat and trans fat increased all-cause mortality. 
Another study made similar recommendations: “Given the strong evidence that these foods lower risk of cardiovascular disease and diabetes, we recommend that men (with or without prostate cancer) replace foods high in saturated fat with healthy sources of vegetable fats, especially olive oil and nuts, which are proven to have cardiovascular and other benefits.” 
by Ronald L. Conte Jr.
 WebMD.com, “Prostate Cancer: The Basics,” WebMD Medical Reference reviewed by Stuart Bergman, MD on February 05, 2016; http://www.webmd.com/prostate-cancer/prostate-cancer-basics#2-6
 WebMD.com, “Prostate Cancer Survival Rates: What They Mean,” WebMD Medical Reference reviewed by William Blahd, MD on November 22, 2015; http://www.webmd.com/prostate-cancer/prostate-cancer-survival-rates-what-they-mean#2-5
 Cancer.org, American Cancer Society, “Survival Rates for Prostate Cancer,” Last Medical Review: February 16, 2016; https://www.cancer.org/cancer/prostate-cancer/detection-diagnosis-staging/survival-rates.html
 World Journal of Urology, Dec 2015, “Prostate cancer progression and mortality: a review of diet and lifestyle factors,” S. Peisch, et al.
 Experimental Biology and Medicine, Nov 2002, “Effects of Lycopene Supplementation in Patients with Localized Prostate Cancer,” O. Kucuk, et al.
 Cancer Research, January 2006, “Chemoprevention of Human Prostate Cancer by Oral Administration of Green Tea Catechins in Volunteers with High-Grade Prostate Intraepithelial Neoplasia,” S. Bettuzzi, et al.
 Journal of the National Cancer Institute, Dec 2014, “Selenium Supplementation and Prostate Cancer Mortality,” S. Kenfield, et al.
 American Journal of Clinical Nutrition, March 2011, “Dietary zinc and prostate cancer survival in a Swedish cohort,” M. Epstein, et al.
 Cancer Causes & Control, Nov 2013, “Coffee and tea consumption in relation to prostate cancer prognosis,” M. Geybels, et al.
 Cancer Epidemiology Biomarkers & Prevention, Dec 2008, “Flaxseed Supplementation (Not Dietary Fat Restriction) Reduces Prostate Cancer Proliferation Rates in Men Presurgery,” W. Demark-Wahnefried et al.
 Cancer Causes & Control, Mar 2006, “Diet After Diagnosis and the Risk of Prostate Cancer Progression, Recurrence, and Death,” J. Chan, et al.
 International Journal of Cancer, Aug 2011, “Vegetable and fruit intake after diagnosis and risk of prostate cancer progression,” E. Richman, et al.
 Cancer Causes & Control, Aug 2014, “Body mass index and weight change in men with prostate cancer: progression and mortality,” S. Bonn, et al.
 Cancer Research: Prevention and Epidemiology, June 2011, “Physical Activity after Diagnosis and Risk of Prostate Cancer Progression: Data from the Cancer of the Prostate Strategic Urologic Research Endeavor,” E. Richman, et al.
 Journal of Clinical Oncology, Feb 2011, “Physical Activity and Survival After Prostate Cancer Diagnosis in the Health Professionals Follow-Up Study,” S. Kenfield, et al.
 Journal of Nutrition, Dec 2012, “Whole milk intake is associated with prostate cancer-specific mortality among U.S. male physicians,” Y. Song, et al.
 Cancer Epidemiology, Biomarkers & Prevention, Mar 2012, “Milk and dairy consumption among men with prostate cancer and risk of metastases and prostate cancer death,” A. Pettersson, et al.
 American Journal of Clinical Nutrition, March 2010, “Intakes of meat, fish, poultry, and eggs and risk of prostate cancer progression,” E. Richman, et al.
 American Journal of Epidemiology, Aug 2012, “Dietary fatty acid intake and prostate cancer survival in Örebro County, Sweden,” M. Epstein, et al.
 European Urology, April 2012, “Dietary Fat and Prostate Cancer Progression and Survival,” Y. Fradet, et al.
 JAMA Internal Medicine, July 2013, “Fat Intake After Diagnosis and Risk of Lethal Prostate Cancer and All-Cause Mortality,” E. Richman, et al.