Sin - rebellion or disobedience, by a free-will creature, which destroys the relationship to The Authority on Life and of Life that has established a rule or rules by which to live by. (Chad's Dictionary)

When did the cancer of sin begin?  
Let us back track.  Today, we know we have rebellion, disobedience, and defiance of God's free gift of love, salvation, and Standard - Jesus Christ.  Rewinding the clock to The Law of Moses, Romans 5:13 says, "...for before the Law was given, sin was in the world." The wickedness of Noah's days displayed this sin.

"When men began to increase in number on the earth and daughters were born to them, 2 the sons of God saw that the daughters of men were beautiful, and they married any of them they chose. 3 Then the LORD said, "My Spirit will not contend with man forever, for he is mortal; his days will be a hundred and twenty years."
The LORD saw how great man's wickedness on the earth had become, and that every inclination of the thoughts of his heart was only evil all the time.
6 The LORD was grieved that he had made man on the earth, and his heart was filled with pain. 7 So the LORD said, "I will wipe mankind, whom I have created, from the face of the earth--men and animals, and creatures that move along the ground, and birds of the air--for I am grieved that I have made them." 8 But Noah found favor in the eyes of the LORD." (Genesis 6:1-8)

So "man's wickedness...had become" means sin must have been around before Noah's days.  It was.  "...death reigned from the time of Adam to the time of Moses..." (Romans 5:13-14) And all Believers know that - "For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord." (Romans 6:23) So sin was around because according to Scripture, sin entered humanity and creation through disobedience to a command of God.

"And the Lord God commanded the man, 'You are free to eat from any tree in the garden; but you must not eat from the tree of the knowledge of good and evil, for when you eat of it you will surely die.'" (Genesis 2:16-17)

What caused the disobedience?  Enter a Narnia-like World with me where, before The Fall, Adam had the privilege and responsibility to tend the Garden of Eden and name all the animals God brought before him (Genesis 2:15-20). Evidently creatures could speak to humans before The Fall because Eve was not shocked when Satan manifested as OR inhabited the body of a serpent (see also Matthew 8:30-31) and spoke. Then Satan, as the catalyst for sin, succeeded at his temptation of Adam and Eve into this dead relationship with God.

"Now the serpent was more crafty than any of the wild animals the Lord God had made.  He said to the woman, 'Did God really say, 'You must not eat from any tree in the garden'?  The woman said to the serpent, 'We may eat fruit from the trees in the garden, but God did say, 'You must not eat fruit from the tree that is n the middle of the garden, and you must not touch it, or you will die.'  You will not surely die,' the serpent said to the woman.  'For God knows that when you eat of it your eyes will be opened, and you will be like God, knowing good and evil.'" (Genesis 3:1-5)

Interestingly Satan did not appear as an angel of light - "for Satan himself masquerades as an angel of light." (2 Corinthians 11:14). Again, he appeared as OR inhabited a serpent. Lucifer had fallen from his lofty position (Ezekiel 28:12-19; Isaiah 14:12-14; Revelation 12:3-4) by the time of this encounter with Eve. This interaction means that Sin lay (past tense of lie) with the Father of Lies or Lucifer in the beginning.

So, when did the cancer of Sin begin? It began sometime after the angelic host were created. It began with an angelic being named Lucifer, who is symbolically referenced as the "King of Tyre" in Ezekiel 28:12-19. Disastrously, Lucifer's miscalculation, delusion, and/or illusion not only caused his own demise but the violent plummet of one-third of the angelic host (Rev.12:3-4) and the death of humanity's relationship with God (Genesis 3:1-5).  

This explanation of where Sin came from is in no way meant to divert taking responsibility for one's actions. The Devil made me do it is very circumstantial. There are times where there is a direct co-relation to one's behavior due to demonic influence. However, it is my personal belief that we are so bad off on our own, before we TRULY accept Christ, that we do not need this excuse the majority of the time.

We call Lucifer - Satan or Devil most of the time. His fallen angels we call demons or evil spirits. BUT GOD.......loved us so much - He sent His angels to help us in times of need, but that was not enough. He loved us so much - He sent great Prophets, Priests and Kings to rule the people and help the fallen condition, but that was not enough. Then one day, God loved us so much He gave us His own Son that whosoever would believe in Him will not perish, but have eternal life (John 3:16).

The mistake was started by one of God's angelic host and continued through our disobedience but it was ended by the Word of God Himself in flesh - Jesus Christ! That victory is manifested in our lives when we accept what Jesus did for us on the Cross and out from the grave. For - "if you confess with your mouth, "Jesus is Lord," and believe in your heart that God raised him from the dead, you will be saved. For it is with your heart that you believe and are justified, and it is with your mouth that you confess and are saved." (Romans 10:9-10)

If you have Not followed the Roman 10:9-10 Path, I encourage you to do so today and then tell me or a local church pastoral team that you trust about your decision.  God bless you all!