So how can this diagnosis be done?
Is it possible to check all organs one by one plus all areas of the body?
What are the early obvious signs?

EARLY DIAGNOSIS OF CANCER AND ITS THERAPEUTIC RELEVANCE
The high potential for mutation of tumor cells limits the usefulness of tissue biopsy as a standard prognostic procedure for cancer because, due to the genetic diversity within a single solid tumor, cells from one end may differ from those at the other and only some mutations are shared throughout the whole mass. Accordingly, a biopsy could miss mutations that might radically change the diagnosis and prognosis of a patient, and although it can provide data about specific mutations that might make a tumor vulnerable to targeted therapies, that information may become inaccurate as the cancer evolves. For an early diagnosis, prognosis, and epidemiology of cancer, it is necessary to detect specific biomarkers that, ideally, should be collected from biofluids such as blood or serum.
Several genetic, epigenetic, proteomic, glycomic, and imaging biomarkers are currently used for cancer diagnosis and therapeutic monitoring, including:
AFP (liver cancer),
Bcr-Abl (chronic myeloid leukemia),
BRCA1/BRCA2 (breast/ovarian cancer),
BRAF V600E (melanoma/colorectal cancer),
CA-125 (ovarian cancer),
CA19-9 (pancreatic cancer),
CEA (colorectal cancer),
EGFR (non-small cell lung carcinoma),
HER-2 (breast cancer),
KIT (gastrointestinal stromal tumor),
PSA (prostate cancer),
S100 (melanoma).

Although proteins are used in the clinic to diagnose illnesses and monitor people undergoing treatment, any of those used as cancer biomarkers are inaccurate. For example, prostate-specific antigen (PSA) can give false positives because this antigen can be elevated in blood for other reasons.

Circulating DNA (ctDNA) in human blood, first reported in the blood of cancer patients in 1977, might perform better than proteins as a biomarker because it bears mutations that are hallmarks of cancer. Circulating tumor DNA is composed of genome fragments that are released when cancer cells die and float freely through the bloodstream, and it could be an excellent cancer biomarker. Unfortunately, ctDNA is not yet ready for a leading role in the clinic, mainly because the most sensitive techniques for its detection require some knowledge about which mutations to search for, and this is a laborious task that must be performed for each individual patient. One alternative is to use exome sequencing, which does not require a previous knowledge about the cancer but is prohibitively expensive. A focused approach to the therapy of lung cancer that would permit keeping costs low has been developed. This approach is based on the identification of a small fraction of the genome (0.004%) that is repeatedly mutated in these cancers. Because almost all patients with lung cancer have at least one mutation in these regions, these mutations may be found by sequencing this small fraction 10,000 times over. The method should work in almost every cancer, except in the case of brain cancers, in which the blood–brain barrier stops tumor DNA from reaching the bloodstream. Unfortunately, the potential of ctDNA as a cancer-screening tool is limited to advanced forms of cancer, which discharge relatively high levels of DNA, but it does not perform well for detecting early cancer forms. It is likely that molecular characterization of a given cancer will lead to the identification of different subsets of cancer disease with a different natural history, sensitivity, and resistance to treatment. In this task, efforts to develop, validate, and implement predictive biomarkers in clinical trials and eventually in routine care are important.

True. Early diagnosis is everything but the challenge is, there aren't symptoms that early enough. Like pain isn't felt until it's at stage 4. Like my nephew he didn't bother with the lump on his breast until it got painful. Then it was too late.

Eh boss why? Mafeelings.....

Umm, by whom? and why?