How to handle serial port incomplete received data?

void comPort_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
//determine the mode the user selected (binary/string)
switch (comm.CurrentTransmissionType)
{
//user chose string
case CommunicationManager.TransmissionType.Text:
//read data waiting in the buffer
string msg = comPort.ReadExisting();
//display the data to the user
DisplayData(CommunicationManager.MessageType.Incoming, msg + "\n");
break;
//user chose binary
case CommunicationManager.TransmissionType.Hex:
//retrieve number of bytes in the buffer
int bytes = comPort.BytesToRead;
//create a byte array to hold the awaiting data
byte[] comBuffer = new byte[bytes];
//read the data and store it
comPort.Read(comBuffer, 0, bytes);
//display the data to the user
DisplayData(CommunicationManager.MessageType.Incoming, comm.ByteToHex(comBuffer));
break;
case CommunicationManager.TransmissionType.Ascii:
//retrieve number of bytes in the buffer
int bytess = comPort.BytesToRead;
//create a byte array to hold the awaiting data
byte[] comBufferr = new byte[bytess];

//read the data and store it
comPort.Read(comBufferr, 0, bytess);
//display the data to the user
DisplayData(CommunicationManager.MessageType.Incoming, comm.ByteToString(comBufferr) + "\n");

break;
default:
//read data waiting in the buffer
string str = comPort.ReadExisting();
//display the data to the user
DisplayData(CommunicationManager.MessageType.Incoming, str + "\n");
break;
}
}

Please give any idea sir.