New study below .
The case for having an adequate intake of vitamin K is that it is necessary for bone & arterial health. K is a vitamin, which means that it is an essential nutrient. There is no reason to take more K than that needed for bone heatlth. K2 (menaquinones) is preferred because K1 (phylloquinone) has a very short half-life.
From a PCa perspective, a German study  found:
"an inverse association between the intake of menaquinones, but not that of phylloquinone, and prostate cancer."
(Menaquinones are mostly obtained from certain aged cheeses . Unfortunately, PCa studies suggest that dairy should be avoided, but if one must have cheese, Gouda will meet your K2 needs!)
From a recent cell study :
"Our data showed that VK2 significantly inhibited CRPC VCaP cell proliferation in a dose-dependent manner at 48 h treatment in vitro. In addition, VK2 reduced the migration potential of VCaP cells and inhibited anchorage-independent growth of these cells. Our results also showed that VK2 induces apoptosis in VCaP cells. Furthermore, VK2 enforced growth arrest in VCaP cells by activating cellular senescence. Notably, VK2 treatment elevated the levels of reactive oxygen species in VCaP cells. Western blot analysis revealed that VK2 downregulated the expression of androgen receptor, BiP, survivin, while activating caspase-3 and -7, PARP-1 cleavage, p21 and DNA damage response marker, phospho-H2AX in VCaP cells."
In the PLCO study, vitamin K status was assessed from a "Dietary Questionnaire (DQX)"
"The present study does not suggest that vitamin K intake influences the occurrence of total and advanced prostate cancer in the general US population."
The Abstract doesn't specify intake levels of K1 & K2. IMO, the optimal intake of vitamin K ensures the proper transport of calcium into bone & prevents the dumping of calcium into arterial walls. Zero arterial calcification is rare in older U.S. men who rely on diet for vitamin K. It would be nice to know more about the PLCO population.
Vitamin K intake and prostate cancer risk in the Prostate, Lung, Colorectal, and Ovarian Cancer (PLCO) Screening Trial
Margaret Hoyt Michael Reger Andrew Marley Hao Fan Ziyue Liu Jianjun Zhang
The American Journal of Clinical Nutrition, nqy251, doi.org/10.1093/ajcn/nqy251
Published: 09 January 2019 Article history
Vitamin K inhibits prostate cancer cells, and an altered expression of vitamin K–dependent proteins in prostate tumors has been linked to their aggressiveness and progression. However, little is known about the effect of vitamin K intake on prostate cancer in human populations.
We evaluated the associations of dietary intake of phylloquinone (vitamin K-1), menaquinones (vitamin K-2), and total vitamin K with the development of prostate cancer among participants in the Prostate, Lung, Colorectal, and Ovarian Cancer (PLCO) Screening Trial.
Dietary intake of vitamin K was assessed with the Dietary Questionnaire (DQX) at baseline and the Dietary History Questionnaire (DHQ) at the third anniversary of randomization by using high-performance liquid chromatography–based food-composition data obtained from the USDA and published studies. During a median follow-up of 11.8 y, 2978 cases of prostate cancer (including 490 advanced cases) were identified from the 28,356 men who completed DQX. Similarly, 2973 cases of prostate cancer (including 647 advanced cases) were documented from the 48,090 men who completed DHQ. Cox proportional hazards regression was used to estimate prostate cancer risk in relation to the dietary intake of vitamin K.
After adjustment for confounders, dietary intakes of phylloquinone, menaquinones, and total vitamin K, assessed with either the DQX or DHQ, were not significantly associated with the risk of advanced, nonadvanced, and total prostate cancer. These results remained virtually the same when vitamin K intake was modeled as a categorical (divided into quintiles) or continuous (per IQR increase) variable or after outliers of total vitamin K intake (defined as a value that falls above the sum of third quartile and twice the IQR) were excluded.
The present study does not suggest that vitamin K intake influences the occurrence of total and advanced prostate cancer in the general US population.